*He'll be back.
* Sephiroth's anger was with good cause, he was angry...at the human race. For what they had done to him. And wouldn't you be mad to? To have never known the truth? Or your father? Or your real mother? to have never had a real childhood? Human cruelty was what caused all this...Sephiroth was just a victim.
*Cloud only killed him because he was ready to die. Otherwise, Cloud wouldn't have stood a chance!