Wait up, I don't understand why Zack being alive proves anything? The fact that he's alive in another timeline doesn't mean he's not dead in Remake's timeline. That's the whole point of having a separate timeline, so Zack can be "dead" and alive at the same time.
If you look at the iconic moments of the OG in Midgar, you have:
- the opening
- the bombings with the bosses fights
- Cloud falling through the church's roof
- Wall Market - one of the things they considered having big changes yet still happening
- Tifa's rescue
- Don Corneo mansion
- the plate fall
- the Shinra tower
- Aerith's rescue
- finding the President's body in his office
- the run away from Midgar in itself
Plus, generally speaking, boss fights. And I mean, all of this is in the Remake. They all went through more or less big changes, were updated, but they were here. Maybe you don't really realise, but generally speaking, the game was acclamed. Fans loved it - in comparison, very few fans were ranting, some even went from ranting to accepting it. Were there big changes? Well, yes. But the OG frame is still here. It will be the same. They've said it since the *first* Ultimania that was released, and again and again. I do not believe that they're lying just to "keep players". They're not interested in that. They're doing their thing, they want to add a twist to the story, how it will resolve we will see, but upon seeing people being hopeful for even bigger changes in the story, of course they'd warn us that "hey, you know the story of the OG will be respected, right?"
IMHO the reason why they've been hammering that lately is because there are too many theories that are just *out there*, from Aerith surviving to changing completely the story. No, they're saying "don't theorise that, you'll get disappointed if you truly believe in that. All the iconic moments are going to be there." They're saying "expect Aerith to die, the Northern Crater to happen, the Lifestream scene to happen".
What do I expect from the next game? The Kalm flashback, the chocobo farm, the mythril mine, the Junon parade (imho Fort Condor can be skipped until the search for huge materia), the ship, Costal del Sol (as the fun chapter as Wall Market was), etc., etc.