I am a bit dubious about this in the world of The OOTS.
Spoiler: SOD
Solely because I have difficulty imagining what unspeakable evil Xykon (and Redcloak) could have gotten up to in the situation where Xykon became a Lich - as such I find it possible that the ritual might have been more like one of the non-evil lich varients that occassionally pop up.