I don't even particuarly care to theorize about what the ending of Rebirth means, because post-Remake, everyone was going wild with their theorycrafting (special shout-out to the geniuses who predicted the devs would kill off Tifa instead of Aerith this time, in a groundbreaking twist that's totally not misogynistic at all!), but then Rebirth pretty much just followed the OG beat for beat (with some significant expansions/additions, just like in Remake). I've always cared more about the characters than the lore, so I'm happy to wait to see how it all plays out in 3-4 years.
Ultimately, whatever it means will just enhance/expand our understanding of events that happened in the OG, without contradicting it in any significant way, so all the major plot beats from the OG will still take place. The ending makes it clear that we're still obviously heading towards the Northern Crater early in Part 3, so I don't see why the rest of the events from disk 2/3 wouldn't just play out roughly the same way as in the OG a la Remake/Rebirth.