I'd be surprised if Sephiroth even tries to kill Aerith this time around. He's quite unhappy with how his plan worked out in FFVII, after all. With Sephiroth working hard to bypass the destiny being enforced by the spectres, it's not inconceivable that the party finds itself in a position not unlike the Avengers in Endgame, where the only outcome they succeed is the one that Aerith dies, but with the twist that the Thanos of the story knows and needs it not to happen.