I think it's rather important to keep the undead Source addicted in one way or another. Being dependent on consuming others' soul/life energy in order to sustain yourself adds a whole new gameplay dynamic and a whole new dimension for roleplaying. And no, it's not the same as being a dark sourcerer and consuming bodies or ghosts to replenish your power. Restoring your (un)life is a far more vital necessity, and a far better justification for preying on others, which makes it much more morally ambiguous and thus much more interesting.
