Such a wonderful manga, thanks so much for the translation! Lots of interesting threads that the author has painstakingly laid out starting to come together in interesting ways, great to see.
One thing I've been thinking about though since last chapter is that the Priestess might possibly be lacking a little in imagination when it comes to magic. I don't know if the time travel efforts by Ida will come to anything, but even 30 years later one game I'll always remember called Chrono Trigger had (among many other great bits) a really fascinating take on this. There is an optional quest you can do to revive the dead, but what really struck me about it is that it's not merely some powerful magic or technology, but a simple magic trick using powerful magic/tech. Like, say someone can make a mindless clone of a person given a DNA sample, and use magic (or even tools/makeup) to replicate scars or tattoos or the like they get. Well, that doesn't accomplish anything to recover the dead, who we are is about our minds and (in these settings certainly) souls, a body clone husk isn't a person. Now imagine you see someone killed, shot through the head or struck down with a sword. Their body hits the ground, their life and self extinguished, you can even test the body and it's clearly theirs genetically and everything... but was it them you actually saw die? We'd never question that, we knew it was them up to that moment, we assume causality as a smooth unbroken continuum. And as the priestess says here the past is the past and creates the present. If causality can be violated either it'll mess up the world or if it's the Everett many-worlds interpretation of quantum mechanics is correct it'll create a new timeline but the old one will continue as before and become inaccessible.
But now take someone who can control time. They jump back to the past and just before the death would happen, they swap in that mindless clone husk, which then gets "killed". Everyone sees it happen just as before, even them, the timeline is apparently unaltered. Except they've played a prank on the universe, a simple sleight of hand to accomplish the otherwise impossible. They've <revived the dead> in outcome, but they haven't actually revived the dead so much as <the death everyone thought they saw never happened in the first place>. They're playing with the gray space between "what we think we observe as reality" with "what is actually reality". I always thought that was a neat approach to an age old idea.
So perhaps the story will be that of moving on to the future too, but the truest magic also often seems to hinge on the truest dreams and imagination/creative thinking, so perhaps there will be options yet that experts haven't imagined.