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?
The loop is closed on our end. Whatever happens in the past should not impact our timeline, as nothing seemed to have impacted Raha's original timeline per the Tales from the Shadow story "An Unpromised Tomorrow". Raha was sent back into the past, but nothing happened to the residents of his timeline when the tower sent to the First - their timeline continued onwards.
We have the answer that Hermes was looking for.
Venat was convinced that he would react negatively to learning what happened at Ktisis Hyperboreia, but we have additional information now that should convince him to help the Ancients. And it would allow Venat to get the Convocation's help, instead of keeping them in the dark.
Moreover, we can still consistently go to the past - to Elpis. More than few of the quests that can take place after finishing the MSQ seem to imply that this is a dependable ability to do so for reason. We're still going back to help Themis with Pandemonium.
It doesn't feel like we would just leave things as they are. As is mentioned throughout the story - "To ignore the plight of those one might conceivably save is not wisdom─it is indolence." It doesn't feel like it would matter whether or not our aid would change anything, it just feels like a loose end to be taken care of. What would be the lore reason for us not to follow up - as heroes?
I also kind of want to see Amaurot at its zenith.