As far as I remember Sven said in one kickstarter update vid, that the Undead in fact would be just a playable race that would have a special ability regarding death. So if an undead character gets killed, something unique shall happen. Of course he didn't mention what exactly would happen to Undeads when they die. They also will have a unique character with an origin story though.
That's at least what I remember, I may be wrong.
