User blog comment:Miskos3/Fairy Tail 539: World Destruction, Review/@comment-7418318-20170616061451

So all the DS have basically been sucked into the Ravines of Time by Acnologia and we all know they'll defeat him in there, probably by killing him... but what then?

It was Acnologia who got them in there, but how are they going to get out again after dealing with him?

My theory on that is on Lucy and Yukino. They'll use the Celestial Spirit World to form a temporary pathway.

If Mashima wants to go for a reverse Rave ending, he could have Yukino stay in Earthland as the exit point and Lucy traveling into the Ravines to create the entry point of the portal for the DS, but then be unable to get out after everyone else went through and be stuck there until the epilogue.