I love all these victories against the pirates. They've got their ass kicked so many times. I can't wait to see the look on their face when the Sea God dies.
After Isma throws the compass in his face, he says that if he weren't a tentacle he'd be dead. Later on his crew tells him that they don't want to die twice and that if he wants to do it, he should do it alone. As they leave, he says "see you again". Then Magnifico asks if it's finished.

Inside the Sea God, Guts comments on how the air is heavy. He can't breathe well. His body feels heavy, like being in water. Schierke remarks that the heart is palpitating faster.
Whoa, that's super cool. I love the panels of the insides of the Sea God a lot. I'm interested to learn what the Captain says during the battle because for them to retreat so easily is suspicious.
He says they'll meet again, but really, there's nothing suspicious about their retreat given the beating they took. And the sea slugs you mention were unable to attack because of Farnese's spell.
EDIT: Another thought with regard to the Sea God to come out - I know there's mention of it being aggravated perhaps because of Guts' intrusion inside especially because it can figure his intent to kill, but maybe the Sea God is out to sort of attack the ship or hold that against Guts' success inside. "If you kill me, I'll swat your friends out there like a fly ... so get out!" - something on those grounds?
There's no reason to think it was aggravated by Guts' intrusion before he reached the heart (since it has eyes and can seemingly see Guts directly). As for attacking the ship, I think it's doing so very simply because its "beard" can't reach it and has been beaten back yet again. It's probably (and logically) pissed off and has decided to end it once and for all. I highly doubt it's planning on bargaining with Guts in the way you describe...
I was thinking the same thing, however, I was thinking maybe along the lines of schierke's having to use her powers to help guts.. perhaps the sea god senses this and is attempting to disrupt guts's activities through reaching her.
Again, that seems a far more tortuous reasoning than the logical course of action I described earlier (tentacles can't beat the ship, so the Sea God is going to take it on directly).
Maybe. I'm inclined to think it's not in the best interest of the Sea God for him to have Schierke separate from Guts in their current attack-mode. It'll get Guts to go wild uncontrollably, killing the Sea God quicker X'D.
Honestly, I'm pretty sure the Sea God's heart is done for no matter what happens outside. However, octopuses usually have 3 hearts, and the one Guts is facing looks pretty small to me compared to its size, so he might have to hack a few more hearts before the thing dies for good.
I'm guessing we'll get to see the Sea god in the next episode (i think he will be quite pissed off because Guts is messing with his heart
)
And because its "beard" has been mangled some more, like I've been saying.