Skin changer liches?

The two most feared subsets of mages are liches and skin changer witches, both types of creatures are considered blasphemous to most Scarterrans by nature of their very existance.   Liches of course are spell casters who have undergone a ritual to become free-willed undead retaining all their spell casting prowess and able to grow in knowledge powers.   Skin changer witches are mages who increase their mystic power and physical might through ritual cannibalism.   Chances are a lich is not going to be morally offended by the actions of a skin changer witch and visa versa. Once a person commits one blasphemy against the natural order, it becomes that much easier to commit a second. So why aren't there more skin changer liches?   A lich cannot become a skin changer witch but a skin changer witch can become a lich. The simple reason is that liches do not eat, so liches cannot engage in cannibalism. Even if a lich "feeds" with some form of magical energy draining attack it is not quite the same.   Most skin changers are hedonists of a sort with more physical vices than just cannibalism. Skin changers may be evil and perverted, but they still like being alive and believe in living life to the fullest in their own sick way. Liches cannot enjoy most of life's pleasures. Many skin changers would rather die than give these things up. As a result, many skin changers opt to not study necormancy at all and those who do, rarely focus on necromancy above the other seven schools with the level of focus needed to become a true lich.   Assuming a skin changer witch fears mortal death more than they fear losing their mortal pleasures, they have a new problems. Incipient madness. Skin changer witches and liches are already prone to madness but this mental deterioriation exponential faster when the conditions are combined. Besides having two independent sources of madness, a skin changer lich has a spiritual addiction to cannibalism that it cannot properly fulfill.   Skin changer liches are very powerful but the don't last long as they metaphorically self-destruct and attract many enemies very quickly. At this point, skin changer liches are well documented enough that few mages are crazy enough to try this anymore.