This is more out of curiosity, but could a mind flayer become a lich?
Not a normal lich, since he's an aberration, but there's still a special Illitid lich template (I believe it's called "Alhoon").
Originally Posted by Winterwind
Mewtarthio, you have scared my brain into hiding, a trembling, broken shadow of a thing, cowering somewhere in the soothing darkness and singing nursery rhymes in the hope of obscuring the Lovecraftian facts you so boldly brought into daylight.