Board Thread:Lore Discussion/@comment-24098614-20150903224652/@comment-177.34.181.193-20150904004646

Daedra cannot actually be killed in Mundus. A Daedra that dies physically in Nirn will just have its soul returned to Oblivion. To get rid of Daedra once and for all you have to kill him/her in Oblivion, which is quite a difficult task.