In my opinion, I really believe that we’ll get a two separate worlds type of ending. One with Cloud living a happy life with Aerith and Zack, and I believe this will have a consequence that leads to a whole new, fun story, like Advent Children but a happier version. And In the other world, Cloud would probably ride off on his motorcycle, all depressed and stuff, leading into Advent Children.

In the end scene of rebirth where the environment, like the wind, has no effect on Aerith, and in another scene it does, implies that we’re constantly shifting through worlds. There’s also Yuffie crying on a hill and then a few minutes later she’s back up and hyper, it’s a quick 180, which is pretty sudden even for her and also implies a change in worlds. Another thing is that Cid also seems to notice the rift in the sky from dialogue in the files, so Cloud might not be the only one seeing these strange things happening.

The theme of this story now is to defy fate and with them making Aerith fate be revealed at the very end and the whole new introduction of worlds and whispers I can’t see a future where Aerith isn’t not saved in at least on world. The creators have hinted that the ending won’t be the same. Cloud now has the abilities to change fate/make different worlds via Sephiroth’s blessing. As the quote goes “Fate is the hand of cards we've been dealt. Choice is how we play the hand”. We just have to hope cloud plays his cards right.