Basically, my prediction is that the entire Zack subplot in connection to Cloud is going to be redone entirely as a way of keeping all audiences in suspense. A lot of fans have asked, "how could they release Crisis Core which spoils the important twist about Cloud's identity, also keep Zack being dead in CC's ending and somehow have it still make sense within the Remake?"
Because CC's depiction and revelation about Cloud won't matter.
The set up is now Zack is supposedly alive out there, based on Aerith's intuitive feelings from the Planet, Cloud's fragmented falsified memories and the endings we've seen so far from Part 1. The hook however, is that Tifa knows something is seriously wrong with Cloud's memories and they're unreliable. However, what's real and what isn't is going to be blurred for them, because there have been other characters surviving events they should not have, like Biggs. The hope that Zack is alive will ultimately be shown as an illusion due to the manipulation of Sephiroth, who will poke holes in Cloud's incorrect recollection of his past, identity and Zack's identity, utilizing the Planet's own record of reality and history. And it will be shown that the Sephiroth who existed in Chapter 18 isn't "real;" he's a thoughtform memory from the Planet that's become sentient due to his indomitable will, based on Sephiroth's past, present and future. Similar to how the Zack that they'll see and believe to have been alive, is nothing but a thoughtform memory based on the illusory past that was mistakenly created.
