I have one.
after Aerith dies she has unique text during certain parts of the game and yet people on the web say that they have proof that square didnt intend for aerith to be playeable after disk 1.
So your question is what exactly?
Square released FF7 pretty much as is was meant to be with minor changed near the end production phase of the game, Aerith dies during the storyline at the exact point on the disks she is supposed to, otherwise the game wouldn't make much sense.
Aerith was always designed to be a playable character right up until she dies, that was the entire point, to create a sense of loss for the player to lose a character that they have spent time using.