Board Thread:Lore Discussion/@comment-11296535-20130914180002/@comment-24489208-20130914181653

It is likely he isn't actually properly dead and he is just in skeletal form so that Alduin can create him again, as with all Dragon.

The problem is that his head is on a wall and his body is in the earth, even for an Immortal, that seems to be quite the predicament. Nevermind that his body is inside a heavily guarded city palace that the Dragonborn goes to often. and the fact that he is completely mad so Alduin probably doesn't want him any way as it is unlikely he will serve under Alduin loyally. It is possible that Alduin actually feared Numinex due to his madness so decided it was best to leave him alone. Not that he would of been able to get to him due to the fact that a load of guards are there AND the Dragonborn is there.

So there are multiple reasons why Alduin couldn't bring him back.