The 8th umbral calamity

[Enkidoh]

It's not a time loop per say, but a branching timeline based on the 'many worlds interpretation' (aka, paralell universes), in our current or 'new' timeline the 8th Calamity never occured, and now never will (especially with

all three of the Unsundered Ascians now defeated/killed for good, Venat/Hydaelyn gone forever and Zodiark completely destroyed, so further Rejoinings would serve no purpose, and the Empire destroyed, Varis dead and Black Rose's production shut down for good.).

But yes the Crystal Tower from the original '8th Calamity' timeline still exists, and as one of the stories on the Lodestone confirms, it's now an 'alternate timeline' seperate from the one the player's character is now on. 'Set adrift', to use G'raha's words, but still existing, which is why Future!G'raha/the Exarch and the Crystal Tower did not disappear - the timeline they came from still remains but no longer one the 'present' leads to.

Whether it will play a role in future storylines or just remain yet another orphaned plotline remains to be seen though.