Rakshas will return and he will ally with Guts
My theory is that Rakshas will be an ally to Guts in the coming conflict. I will say upfront that there is some reaching going on in this theory, and you may not agree with my interpretation, but I will at least start with facts and explain my reasoning from there. I will also preface by stating my assumption that there exists a sense of respect, understanding, and competence of Miura’s work by those heading the continuation. Call me an optimist.
I will separate this into two parts: 1. Why I believe he will return to the story after the events of Ch. 380. & 2. Why I believe he will align himself with Guts.
Part 1. Loose End
At the time of writing this (release of Ch. 380) Rakshas has seemingly been slain, rather unceremoniously, by Silat. However due to the circumstances of his prior return / revival in Ch. 377, I believe that we will see him reappear in a similar fashion. (I will refer to his reappearance in Ch. 377 as his revival, as Rakshas himself assumes he died, although it is possible he is mistaken).
I won't argue that him not reverting to his human form and being taken by the vortex of souls is indicative at all of his death, as we saw in the attack on Flora’s cottage that does not necessarily always happen when an apostle dies. In any case, I am arguing that Rakshas is not dead, or at least is not dying in the traditional sense and so this point is moot. I will also not argue that Rakshas is anything but an apostle, as that idea is not supported in any way. Rather I will point to the narrative need for certain questions concerning Rakshas to be answered.
We have no understanding of how or why Rakshas seemingly revived out of nowhere in the Kushan temple, with him even being confused himself. That indicates that he is being used by a force beyond him, like a Godhand member. I do not bring them up lightly, but we have no reason to suspect that Rakshas is capable of opening a rift to Qlipoth. Unless we get some sort of indication that it can happen another way, we can only assume Slan is to blame for this. She would afterall surely revel in the pain Guts is experiencing. This event is very different however from the first time we encountered Qlipoth, but it is the strongest lead we have.
With both Rakshas’ revival and the rift being opened seemingly simultaneously, I believe we can assume the two events are linked. The only real reasoning I have for this is the link between Slan and Qlipoth already established, and the logical conclusion that narratively they are retreading old ground for a reason and not just reusing assets to spawn fodder for an action sequence. Again, giving the continuation team the benefit of the doubt on this one. If he is being used, then it stands to reason that whatever use that is, has not been fulfilled yet as Rakshas did not achieve much of anything before being put down by Silat, therefore Slan/whomever is cursing him, will revive him again.
Narratively speaking, it would not make sense for them to introduce this resurrection idea in the first place if they did not plan on answering it. They could have just as easily had Rakshas infiltrate of his own will to enact revenge on Silat/Rickert for the blast to the face. The mystery of his revival is a loose end that needs to be tied up, and since Rakshas himself questioned it, it stands to reason that he will be given some closure. My reason for this is because nobody else will question this return as they all assume it is a strategic attack (which very well could have been, just not one orchestrated by Rakshas). They may even assume that Rakshas survived Rickert’s blast due to him being able to conceal the location of his head (a fact he surely would have mocked Silat over if that was the reason for his return, as he did in Falconia).
On that matter, his ability to move his true head around may even be the method in which he survives this “second death” at the hands of Silat, or could be a Red Heron to distract us from the theory that a higher being is controlling the situation. Therefore it makes more sense for Rakshas to return either by the same force that enacted his first revival, or by way of his own abilities to fake his supposed death by the hands of Silat, perhaps biding time till the moon rises, as he does in Ch. 339 after Silat slices through one of his masks while protecting Rickert. Simply put, for these chapters to make any sort of sense whatsoever for the overarching story, there has to be more to come from this mystery, and any sort of answer will require Rakshas to be present as a vehicle to deliver that explanation to the readers.
Part 2. The Enemy of My Enemy…
There is more than one unanswered mystery concerning Rakshas. His past as a member of the Bakiraka has been mentioned several times, as well as his subsequent banishment. To top that off his rivalry with Silat seems to be in full swing, with little dialogue being traded between the two after his revival in the Kushan temple. That could either be a sign of Mori and the continuation team not being able to write dialogue between the two of them for some reason (not enough info provided to them from Miura) , or maybe it is because this was meant as a confusion filled, strike first ask questions later altercation where no dialogue was necessary or even possible. The confusion and anger we are all feeling, as voiced by Silat at the end of Ch. 380, was purposefully created to blindside us with an unlikely alliance.
The elephant in the room however is Rakshas’ desire to Kill Griffith himself. There isn't much that I can say on this that Rakshas hasn't made abundantly clear himself, and that is that he will take Griffiths head himself one day. See Chapters 184 and Chapter 340. This alone does not mean Rakshas will ally himself with Guts, but it does come halfway. For the other half we need to look at Guts.
Guts story has been about accepting help from people around him, and valuing their lives as his was not. It's about giving when you have nothing left to give, fighting when you have no fight left in you. Changing yourself for the better for yourself and those around you. Guts even allied himself with Zodd temporarily to beat Ganishka when his life and the lives of his friends were in jeopardy. It is the antithesis of fighting unnecessarily, and all about seeing the good around you to protect what you have not yet lost. As Puck stated to Vargas way back in Chapter D0, “living for the future is more important than avenging the past”. Guts accepting help from an outside source he should by all rights have an unyielding desire to kill (or be killed by apparently) is a step into that direction that Griffith is incapable of. Griffith sacrifices those around him for his own gain while Guts sacrifices himself for those around him, with him constantly taking hits for those he cares for, further exemplified by the Berserker armor eating away at his life every time he uses it. Griffith is none of these things, he is the “Blazing inferno” that the “little flames throw themselves into” (Ch. 22). He uses those around him as his stepping stones to rise to greatness, while Guts allows himself to be used for those around him to find security. The point is that Guts does not consume or overshadow the flames around him, he ignites them, and that is why Griffith will lose support while Guts will gain it.
The idea of apostles turning away from Griffiths is not only shown by Rakshas, but by Zodd as well. Along with the aforementioned temporary truce, Zodd is unlike other apostles, he doesn't seem to have the same type of natural subservience, as he did not immediately follow Griffith the person, but rather follows his strength. Rather he follows his own desires that allign himself with Griffith. In his quest to find the "Ultimate Strong One" he has allied himself with Griffith, all the while harboring a certain respect for Guts as a warrior. I believe Zodd will no longer follow Griffith soon, as he sees the weakness in him via the moonlight boy. Griffiths most vile deed coming back to haunt him, serving as the chink in his armor that crumbles his defenses, with Zodd leaving as him losing his ultimate defense. I'll admit this is where the reaching comes into play and you may not agree with my interpretation of Zodd here, fair. I also recognize that there is groundwork laid for apostles rebelling against Griffith by Ganishka, but I assert that Zodd is unique in that he has expressed ulterior motives, does not partake in the type of senseless acts that other apostles do, and therefore will be able to "break out" of his absolute adoration. If the redacted chapter is to be believed, then perhaps Griffiths power may lessen due to those around him shedding their fear/respect. All I have is Zodd and Guts' relationship, and I pose the question of what exactly does Zodd value in a warrior? Will Griffith maintain that status or will Guts exemplify the true warrior spirit, enough so to sway Zodd? If the story's aim is to delegitimize Griffiths actions and praise Guts' then the answer is clear.
Obviously this would be a problem with Skull Knight but that is why they may not necessarily fight alongside Guts but rather will not work to thwart one another, or perhaps I'm jumping ahead and they will only find themselves allied at the eleventh hour in the finale. In any case that unyielding vengeance Skull Knight may show would only further prove the growth that Guts has achieved, and how he has succeeded where Skull Knight has failed. Further ideas for this point is the theory that Guts will save his love where SK could not, and that Guts will wield the armor with more control than SK, thus retaining his humanity but at the cost of his revenge. That is another theory by itself. it is also my belief that both Zodd and Skull Knight are cautionary tales for Guts' future, and will rise above them. Allying with select apostles, would be the catalyst for this.
This shift in allegiances is made more likely narratively due to it potentially solving multiple problems. That is where the wildcard Sonia comes in. Shierke is currently looking for Casca in Falconia, but what will she do once she finds her? Schierke and Sonia had a meeting in Chapter 246 where they made friends with one another. I believe that will become relevant again as Sonia may be able to detect Schierke while she is surveying in her astral form. She may even converse with her and have evidence shown to her of Griffith's true nature, either from Schierke or Casca. Sonia may just be the ace in the hole that our team needs. Not to mention the dramatic irony in Griffiths most staunch supporter turning against him. Sonia may not be too keen on allying herself with Kushans after what happened with her parents (Ch. 182) but all the more reason she may not come into direct contact with our group for a while, she would be more useful as a spy or as a friend to Cascas and/or facilitate her escape. With the prospect of gaining an edge over Griffith, along with assurance that Casca is still safe, that may be just the right push for Guts to overcome this crushing defeat, showing that all of his work was worth it, as the little flames he has stoked this entire time have come back to reignite him. As Guts finds the strength to continue fighting, he may even remember Godot's words to him, wouldn't that be somethin.
We are coming to the end of the story and there will need to be some things that happen before the scales are tipped between Guts and Griffith. It fits the themes of Berserk for Griffiths power to erode as it is ill gotten and unsustainable, while Guts reaps the rewards of all of his hard work, with the help of those around him. That is why I believe we are amidst major turning points in the story which will make minor details / interactions from dozens/hundreds of chapters ago relevant now more than ever.