User blog comment:Madman97/The Aedra Vs. The Daedra theory/@comment-3025184-20131010203442/@comment-9062114-20131011060017

The Dragonborn never killed Alduin. A mortal can't "kill" a god (maybe if a Dragonborn gets powerful enough he could, but I digress). He just destroyed his physical form. Both Arngeir and Paarthurnax say he's still alive. Paarthurnax as I said, probably didn't find it necessary to explain exactly what Alduin is.