Last I checked getting Sephi was a confusing affair. When you do get him, he is exactly as he was in the flashback.

And that Aeris thing sounds like BS to me, though for some reason she does have lines programmed into the game after her death. I believe the response I got when asking why at the FFOnline forums is that Square started programming the game from the middle, and hadn't worked in where Aeris would die yet or summat like that.

I'm sure if I'm wrong someone more enlightened will tell me.