If I remember right,I though I read somewhere that Sephiroth controlled Jenova.I don't think a fall was enough to literally kill Sephiroth.Though it is said in the game (I think by Hojo but am not very sure...) that the "real" Sephiroth died in the reactor.Since Sephiroth is a SOLDIER,SOLDIERs are more resistant than average men and can take a lot more damage.Therefore it is obvious he wouldn't die from being cut by Cloud who wasn't that strong.So it seems he died from the fall into the lifestream(?).But I don't think that his body was destroyed.Why?Because Coud too fell in the lifestream and he came out of it pretty much with every body part.
Therefore Sephiroth's real body may continue to exist if he was "washed out(?)" somewhere after falling in.Now...I do believe that the crystallized Sephiroth is th real one.To me he seems like was "hibernating" in a way,as Jenova was carrying out his orders to summon the Meteor.But it wasn't jenova acting on her own,in fact I think Jenova,when it comes to power,is overwhelmed by Sephiroth(for some reason I am sure I've come across this somewhere...).I believe Sephiroth was "hibernating" to reach his full potential and maybe he could only exist crystallized in that time since later he is REBORN as a god(am I right?).Maybe that's why he didn't do what he had in mind and had Jenova follow his orders.
So I am guessing he was weakend by the fall in the Lifestream but didn't die.
I am not sure if what I am saying is valid,because I haven't really read any of the extra stuff that was written during the release of the FFVII:AC about Tifa,Denzel and whatmore that provides more information and insight in the storyline.Also It's being over a year since I played FFVII and I never wondered about this,so this is the first time I am trying to get more into depth.I hope this all makes some sense.
Therefore Sephiroth's real body may continue to exist if he was "washed out(?)" somewhere after falling in.Now...I do believe that the crystallized Sephiroth is th real one.To me he seems like was "hibernating" in a way,as Jenova was carrying out his orders to summon the Meteor.But it wasn't jenova acting on her own,in fact I think Jenova,when it comes to power,is overwhelmed by Sephiroth(for some reason I am sure I've come across this somewhere...).I believe Sephiroth was "hibernating" to reach his full potential and maybe he could only exist crystallized in that time since later he is REBORN as a god(am I right?).Maybe that's why he didn't do what he had in mind and had Jenova follow his orders.
So I am guessing he was weakend by the fall in the Lifestream but didn't die.
I am not sure if what I am saying is valid,because I haven't really read any of the extra stuff that was written during the release of the FFVII:AC about Tifa,Denzel and whatmore that provides more information and insight in the storyline.Also It's being over a year since I played FFVII and I never wondered about this,so this is the first time I am trying to get more into depth.I hope this all makes some sense.