"The sheep have killed their sheepdogs here, so I don't think the comparison applies. That was the result of them beating them in the end." The wording of this sentence is unclear to me.
Sephiroth absorbed the Whispers for the final battle and became "Fate" itself. He was then pushed back to the point of losing control of them. After the fight, they all explode in a flash of white light. We see this explosion from Zack's perspective, and the Whispers that surrounded the Shinra Building (that Rufus could see as well) are all gone. The Whispers that were surrounding the entirety of Midgar in a dark dome in the present are also all gone, and in it's place, the golden snow falls down. This happens in Zack's time period too. They've been blown away.
And for all those who bring up Kingdom Hearts in comparison to the speculative time travel/AU elements that exist in the Remake, the KH series' concepts for time are actually pretty solid and straightforward. More so than
this. In KH, the time travel only happened when a person's heart/essence went back to the past where they existed and any time travel done did not carry over the memories obtained. Furthermore it only was used to explain the appearance of characters from the past reappearing in the present. There was never an AU/split there.
Zack is around to show up whenever stuff wants to get all metaphysical on us, just like this ending sequence. I can't imagine it'll be anywhere close to the last of these sequences. I think you underestimare Zack fanservice as a goal in and of itself, nothing in my eyes was gained by making Advent Children about him in the new version but it still happened, but obviously, there's no putting the genie back in the bottle.
I get the Zack fan service, and Zack being included in the ending at all exemplifies the fan service. A convoluted and unrealized AU explanation seems entirely superfluous; it's not needed for him to be there. Again, it's like
Chekov's gun; if you show it, you use it. Zack's appearance in ACC was to encourage and give Cloud the needed strength to get back up and fight Sephiroth in a duel that was far less sanitized and far more life threatening. Aerith appeared as a ghost in that movie, alongside Zack talking to Cloud. So him appearing in the director's cut makes sense and uses him since he was already.
What I'm getting at, is if an AU only exists to showcase Zack being "alive" (although technically that wouldn't
be Zack, it'd be Zack-X from another universe) and that's it, then that's a complete waste of such a heavy concept. If the AU is there, then by that train of thought, we're either visiting it, or it's coming to the heroes. It won't just be symbolic, that means the AU is going to play a role in the story.
I mean I don't remember this epic fall you are talking about. Did we see Wedge again after he was being harassed by the whispers?
Wedge was shown being blown into the Shinra elevator shaft and on the cut to black, the loud crash of glass breaking can be heard.
Maybe Zack got snatched up by the Turks and he managed to hide Cloud from them and left the sword with him or something. I feel like there's a way to get Zack out of the way to have the setup for the story remain the same but he's still alive to return for pointless dumb fanservice at some point
That still presents a plethora of issues that aren't simply handwaved away. The Turks wanted to
save Zack. That's why Reno and Rude were dispatched to find them first, however they failed and the Public Security army found Zack first. If the Turks accomplished their mission of finding him, why would Zack have to be hidden so far away alone? Where would that even be? He wouldn't leave Cloud behind, nor would he leave Aerith behind, not without at least telling her he's okay and still in love with her. And he certainly would
not leave his sword behind, that
never happens. The entirety of Crisis Core's final act is him making a bee-line to Aerith so that he can lay low, tell her he loves her still, and take care of Cloud.
Aerith doesn't know what happened to Zack. Tseng wanted to get Zack back alive and give him the letters that Aerith wrote to him. Why would Tseng not tell Aerith he was
alive when his desire was explicitly to
do that? There's no way you can reconcile the story of Cloud and Aerith in FFVII with Zack just magically being alive in the same time-stream. It's not just a total contradiction. It's a paradox.