Board Thread:Off Topic/@comment-25143792-20140712044007/@comment-5989209-20140712053820

If they are "killed" on Nirn they go into Oblivion to reform, and if they are killed in Oblivion, they do not die for ever but they are significantly weakened to the point that they become non-factors, just like any Daedra. The same is true of Daedric Lords, however they are significantly more powerful, having bodies as well as being a part of their plane. Take Shegorath, he is the Madgod as well as the Isles themselves. Atronachs don't have that privilege so it's easier to remove them.