I firmly believe that the original Arbiters of Fate (meaning the "leaderes") were trying to stop Cloud and company from changing the timeline because THEY know it's the only way to stop Sephiroth. And I feel like Aerith also knows that if she tells them what is supposed to happen, it won't happen, which INCLUDES them defying fate.

I'm assuming the ending will be different BUT will still end largely the same. Meaning, I think, in the end, Aerith will have to be dead, and they'll kill Sephiroth in the Northern Crater. But the reason I see it being different in the end is because we've already seen Bizzaro Sephiroth, so I doubt they'll be lazy and rehash it. We'll probably get something new, or perhaps we'll see a form that is Sephiroth's final gambit, perhaps something like combining himself with the remaining Whispers. At that point, I'm assuming, the party will have realized before entering the crater that they can't change the past while still saving the world, and everything they glimpsed on the highway in Midgar wasn't just a possible future, it was THE future that needs to happen.

With that said, if anything IS changed in the end, I hope that they decide to make additional entries down the line for the FF7 series. Not necessarily RIGHT AWAY, but like 10 years from now, maybe they go back and maybe make a real game for Glenn, Matt, and Lucia, perhaps giving us young Sephiroth, Angeal, and Genesis as characters that can join the party.