*Spoilers* The Past and After the Endwalker MSQ End

[Vexander]

So what's keeping us from pulling a G'raha Tia and going back to the past to helped the Venat that helped us avert the Final Days for that timeline?

Honestly? We have no idea how changing the past of the Unsundered World will affect our world. We know that altering the pasts of different shards created different timelines, but the Unsundered world is incredibly dense in aether, to the point it's original inhabitants were outright immune to the effects of Dynamis, while people living in the shards will be transformed by it and be completely lost.

What we did in Elpis was a closed loop of events. Altering the events drastically, as in preventing the sundering of the world, could invariable destroy our timeline and that of the shards, and there's no way of knowing for sure because the Unsundered World's aetheric density is so much higher than ours.