The Daedra are Immortal. Ergo, you will not be killing any of them, because you cannot kill them. You may break their bodies for a time and banish them to the Waters of Oblivion. . . but they will return.. . and they shall mark your name and face!
bliviongate:

There are things worse than death. Such as having your life force be put into a crystal and svcked dry slowly for some haughty spellcaster's enchantments.