Board Thread:Lore Discussion/@comment-71.226.242.68-20131113201112/@comment-24081142-20131113202507

Aedra and Daedra differ in that the Daedra did not contribute to the creation of the physical world, while the Aedra did. Therefore, part of the Aedra's power is tied up in the world itself. Also, as I understand it, Lorkhan is missing, presumed dead, but it is not entirely certain whether he has actually been completely destroyed. Since his avatars (Shezarrines) have appeared at various times in history, it appears that some part of him remains and could possibly be restored by some means.

I suspect that killing a Daedric Lord on their home turf is something of an academic point, since even if it did prove fatal, there's nothing powerful enough to actually do it. The Aedra are presumably weaker than Daedra since they diminished themselves in the creation of the world. Dragons, even Alduin, are powerful but not actually divine - their powers are great but limited, while Daedra appear to be effectively omnipotent in their own realm. Even if one Daedric Lord were able to invade another's realm, the invader would likely be weaker due to being separated from their home plane. As a result, they would be defeated, banished back to their own realm, and nothing would be settled.

There is also some evidence that a Daedric Lord and his realm are one and the same, so just killing the manifestation of the Lord wouldn't be enough - you'd need to destroy the entire realm (and probably yourself along with it)