You clearly didn't bother trying to understand the original suggestion, because it doesn't make liches any more "disposable" than they already are. There is nothing "disposable" about a nemesis that repeatedly comes back from defeat, growing stronger every time, up until you finally figure out how to kill/convert them for good. All it does is undercut the frustration factor of cheaply "losing" to a lich just because you don't have the right mods or sequence yet. Forced, arbitrary failures aren't going to be fun for most players, but struggling with a powerful rival on mostly even footing could be. An enemy that repeatedly resurrects from death would also fit the whole "lich" theme better, IMO.