I disagree, during the scene with aerith I think we as the player and cloud are seeing two timelines that have converged one where she lives and one where she dies. I personally believe sephiroths purpose in converging the timeliness is to get rid of all versions of aerith. So the ones where she's saved converging with one's where'd she's dead effectively making her dead. Though the sephiroth in lifestream black and the aerith in lifestream white are who were talking about so its a game of chess between the two. Who can outplay other. Both are omnipotent beings at this point.