Board Thread:Lore Discussion/@comment-71.226.242.68-20131113201112/@comment-1600847-20160405122758

Daedra can't be permanently killed, they always reform in the Chaotic Creatia of Oblivion after their physical form is destroyed. It's unknown if this also applies to Daedric Princes, as no one's ever really tried to kill one, but it's likely the same rule applies to them.

Even when the Vestige was infused with the power of Akatosh they were only able to severely wound Molag Bal. And even then Bal was all healed up a few minutes later.