Kurzen may be dead, but...that which drove him to evil still lives! Through my studies I have discovered this: An Ogre Mage - Mai'Zoth - dwells in an Ogre Mound within the eastern mountains of Stranglethorn. He is rumored to employ mind-controlling magic, and I am positive that he corrupted Kurzen.
If Mai'Zoth is allowed to live, then his evil may influence others, and may even cause another Kurzen to surface.
Kill him, and bring me his Mind's Eye, the artifact he uses to corrupt others.