Walter said:But what if she was forced back into her body? The force of the wave impact aboard the Sea Horse could jolt her back, or any number of things.
Then that's not a choice she has to make.
Walter said:I don't really think there's any better place for her right now than by Guts' side. Taking out the Sea God's heart should be priority number one. No offense to Schierke, but creating more magical bulwarks against the Sea God isn't likely to have much effect.
Agreed on all counts, and I think she knows it, which is why she won't willingly leave Guts. It's clear she couldn't do anything to help against the Sea God from the outside right now. There's no time, no spirits nearby, and the creature's just too big and mighty anyway. She's remarked on it herself before. And beyond that, like everybody said, without her Guts won't be fighting purposedly anymore, and won't have the presence of mind to escape once the deed is done. She wouldn't leave him alone if only for that reason.
For all the reasons above, Schierke being forced back into her body would actually be a dreadful development. As for the Sea Horse, there is one way it could survive an attack of the Sea God (at least for a little while): to be swallowed whole just like Guts was. Not something for them to look forward to, though.