In the Tales from the Shadows story, Emet seems to suggest that Elidibus emerged from Zodiark as a very different person. It's hard to say in retrospect whether that would have been reversed by looking at his soul crystal's memories, as Amon still very much retained his new identity than the one from his past life.

Quote Originally Posted by Tehmon View Post
Whether we go back to the ancient world though, remains to be seen.
Just a quick note on this. During one of the very first cutscenes in the Asphodelos tier, Claudien tells us the following about the unmarked Lahabrea crystal that prompted this story:

'Not long after the exodus was declared, we recovered an unusual crystal shard during a routine observation. It appeared before us suddenly, as if propelled to the surface by some unknown force.'

Someone likely hurled the crystal into the lifestream in the past. This is Backrix's journal all over again.

If I had to guess, I think the Tartarus story will be split between the two time periods with two different parties, in a nod to FFII.