Upon traveling through the marshes you will be attacked by a group of undead, just prior to meeting Zaleskar. The head enemy undead will speak with you opening up this quest. After killing, speak with Zaleskar to continue quest.
On Nameless Isle, a Voidwoken will offer undead character a chance to serve the Godking. If you accept, this will lead to the Godking ending, unless you use the swornbreaker to free yourself.