Let's play a game: Save the Ancients!

[redheadturk]

I have to thank a friend for this, but there is yet another context clue for the protagonist that the timeline G'raha hailed from still exists: G'raha's memories of that timeline still exist. If the timeline had vanished, the aether that makes up G'raha's memories of that timeline would have poofed too. They didn't, as we'd know because we uh. . .inserted those memories into his younger body on the source?

[Cleretic]

I have to thank a friend for this, but there is yet another context clue for the protagonist that the timeline G'raha hailed from still exists: G'raha's memories of that timeline still exist. If the timeline had vanished, the aether that makes up G'raha's memories of that timeline would have poofed too. They didn't, as we'd know because we uh. . .inserted those memories into his younger body on the source?

Your friend's 'clue' makes no sense whatsoever. For that to be evidence we'd need to have evidence that that's how it works in the first place, and that evidence just doesn't exist. It especially doesn't exist to the WoL, whose knowledge of tiem travel up to that point has been learning G'raha Tia, and probably also doing Alexander; in neither case did this observably happen. Your friend seems to be assuming that it works like other franchises' time travel works, like Star Trek or Doctor Who, but with no evidence that they actually do. ...except in most cases, those franchises also build in sort of an immunity to those effects for the time travellers, including both Star Trek and Doctor Who. Which, if that's how FFXIV works, would also leave G'raha able to remember everything just fine. So even if the WoL is an avid Whovian, this wouldn't register as evidence.

...and all of this is also ignoring that this isn't actually the issue, the issue is that changing the timeline strands you. Which is a pretty crucial thing in this case: unlike G'raha, whose original timeline didn't really have anything important for him to do, the WoL has a very specific job of 'go find out what an Elpis is and then come back and tell us if that's helpful'. I don't care how much questionably-educated faith the WoL has in the fact their home timeline will still exist, that's not the problem: the problem is that if they change the timeline, they can't go back to the one that needs their help.

Frankly, I'm surprised you don't reflexively know this, because the one that said it directly to our face is the Ascian you glorify in your signature. I would've thought that you of all people would've commited his whole thing to memory, but I'll happily link it if you haven't. Incidentally, I do find that it's a pretty poetic use of language by the localizaton team: he warns us that 'we cannot reshape the past', and at first it sounds like it's cannot as in 'won't be capable of', but it soon becomes clear it's cannot as in 'you mustn't'. Which, incidentally, makes more sense given we're using the same technique G'raha used, and we know where G'raha can't go back to.

[Iscah]

I have to thank a friend for this, but there is yet another context clue for the protagonist that the timeline G'raha hailed from still exists: G'raha's memories of that timeline still exist. If the timeline had vanished, the aether that makes up G'raha's memories of that timeline would have poofed too. They didn't, as we'd know because we uh. . .inserted those memories into his younger body on the source?

I don't see how that proves anything that his continued physical existence doesn't already prove (or fail to definitively prove).

In the hypothetical scenario from the characters' perspective that the other timeline was destroyed but G'raha wasn't taken with it, the continued existence of his incorporeal memory-aether is no more significant than the continued existence of his corporeal aether. If one can survive the obliteration of its source, why shouldn't the other?