If Aeris had lived FFVII would have lost one of the most beautiful and emotional moments ever in game history. And that's the truth because Aeris' death has been repeatedly hailed as one of the most sad events in gaming history...bad graphics and all...

AC would also not have been possible...no wait, it would've, just with Aeris in it.

I also think there'd be no obsessed Aeris-Cloud fans who are convinced she was meant to come back and score Cloud...there'd also be more Tifa haters because the Airy Cloud fans would be disappointed with the romantic outcome...

Think of what would happen if Aeris was still alive after the lifestream incident with Tifa and Cloud in Mideel. She would have realised her attraction to Cloud was linked to Zack, that it was Tifa's love for Cloud that saved him and she would've let go and moved on. Maybe hooked up with Vincent?