Should I kill him or let him live..

Post in the dang spoiler board.

If you have to ask that question you just lost the game, friend.

Also: spoilers everywhere!

I think killing somebody based on what they might do is a dangerous way of thinking. Killing somebody for sins committed thousands of years ago after he had turned from his ways and in turn helped all of mankind and assisted the Dragonborn later on is mindless vengeance.

IMO if someone doesn't want to see spoilers, he shouldn't go on this site..

and besides, he won't even know who I am talking about.