Donald Shimoda said:unless he somehow becomes much more powerful I dont know how hes going to defeat Griffith and the God Hand.
I'm not so sure he ever will defeat them, and the way I see it, he'd probably receive a mortal wound during such a battle. Nothing about Berserk has ever led me to believe there is a light at the end of the tunnel. Guts is only in his mid-20's I assume (correct me if I'm wrong) and he already is missing an arm, an eye, has white hair coming in, is losing sensation in his fingertips, is losing sense of taste, is wearing a cursed armor that is slowly killing him, his girlfriend was raped and has lost her sanity, and when she regains her mind she is probably going to use that Beherit in Guts satchel so she can once again be a sword for Griffifth's Army now that he has taken a human form again, she will want to help Griffifths's dream come true. She might not remember the Eclipse, in which case she could very well fall victim to Griffith's charisma again. I quote the Skull Knight in Episode 238: "What You Wish For May Not Be What She Wishes For." Anyway, my point is, don't expect Berserk to have a happy ending....not that it will be ending any time soon. I guess we'll find out in about 20 years.
By the way, the whole Beherit thing I mentioned is just a theory, but it's gotta be for someone, it's with Guts for a reason, and I'm pretty sure I read here that Miura has stated he wants Guts to retain his humanity...therefore it has to be for someone else who is or will be around him.