I think I heard that according to the originales, Cloud was intended to be a half-demon hybrid and Sephiroth was supposed to be his transforming half-brother.
Vincent wasn't intended to have a gauntlet, but instead he was supposed to have a pair of gnarly pistols and return from beyond the grave to take revenge against Rufus who had killed him for "betraying" him in favor of Shinra.
Aeris was originally meant to be Aerith (pronounced Aeris), a whore from the Honeybee Inn who frequented the Seventh Heaven and engaged in regular drunken orgies with Barret and Tifa.
Marlene was never supposed to be human but instead a tiny robot doll designed by Professor Gast and programmed with the intent of studying the "slummers" reaction to prolonged exposure to Mako liquid that provided their towns with energy.
Red XIII was another robot prodigy. Except he was going to be a hulking mass of armor like the robot in Chrono Trigger only red.
The Turks were going to be called True Grave or the Raiths before the Turks was decided.
Originally Reno was set to die when Cloud chopped off his head and threw his corpse off the tower, but that was a little too violent.
Zack was going to be the main character of this game before they decided to kill him. Before that, they intended that Cloud be little more than his underling or effeminate lover.



It doesn't matter that all that's made up as it doesn't matter what Square's original "IDEAS" were, the story went as it was intended to go because that's the way it ended up. It would be saying something completely different if FF7 was based on a book in which Aeris lived. Then you'd be wholly correct in your assumptions.

George Lucas's Star Wars originally had it that Luke be called Starkiller and that Return of the Jedi be called Revenge of the Jedi (which revenge doesn't suit the character of a Jedi). If you say that Aeris was supposed to live because at one point they hadn't created the idea, then you have to say the same for any character in any story that has or will ever die(d).