Let's play a game: Save the Ancients!

[Iscah]

As to the question, G'raha has proven alt timelines exist, all we have to do is #1 leave notice of the threat in a memory crystal in a place Emet or Hyth is certain to find it [their office that people generally don't go into while it's empty comes to mind] or #2 telling Elidibus and Lahabrea after the congruence has finished during the raids [sharing it in an echo vision being the most likely method.] They can then handle it from there with all information in hand.

I wrote about this aspect back in my initial post. From the characters' perspective, G'raha has not proven that multiple timelines can co-exist, only that he can travel from the future and change the past to create a new future entirely unlike the one he came from. He does not know and has no way of knowing whether that first future still exists or whether changing the past has obliterated it.

From that initial state of understanding, any effort to change the Ancients' fate is a 50/50 gamble on wiping out the current timeline to give the Ancients a chance – no guarantees – of surviving, and I see no reason why the characters should be willing to take such a risk with their own existence and the world they've been fighting to save.

And yes, it is an unfortunate mismatch of themes that this gamble is exactly what G'raha was doing with the 8UE, which has always seemed like bad writing – again it seems like the writers were wanting to have it multiple ways at once at the small scale without stepping back to observe the contradictions. They pulled their punches on just how bad things were, when things needed to be irreversibly dire to justify what they were doing.