When quest-giving NPCs die they are replaced by a relative NPC, which makes them the new quest givers.
Now, don't get me wrong, I think it's a good idea and all, but if I kill the new quest giver... will he be replaced with a new NPC?
How many relatives do NPCs have?! Will there be like a million? infinite? I hope eventually the quest dies with the quest giver......
Provided a smart random name generator, they could, in fact, be infinite. Though by the time you kill family member #3 you'll probably have a bounty on your head regardless of whether anyone noticed you. Hence you'll have other things on your mind, like a (&@|*load of guards on your tail. If you're still stubborn even then, well, then it's a madman system for a madman character.
Fitting.