If you read the book of worms (its ok you dont have to its a lot.) You would know (can also just use simple observation skills. You see himself use his own power and enter another realm smiling. Jesus how does everyone forget about the raid) that to kill one of the princes (or the king, brother/sister of the princes) they must reside within their throne realm. Their sword realm i think its also called. If they are not killed in their own then they are able to be reborn through their driven nature. Forgot which but off top of head. Xol roi or what ever was conflict and war. Saventhu or whatever was cunning and wit. And auryx who became King Oryx by killing his brothers outside of their rooms and learned of thier powers (war and cunning w/e) . So ya he isnt dead. We just bested him in this realm where he is in a way immortal