Thanks for this useful guide.
Out of curiosity:
Consider the worst case. You are facing a pre-buffed demilich which has ALL(I mean it) combat and spell protections at once. He is invisible, protected agains ALL schools at once, his magic resistance is 100%, he is invulnerable to all weapons and all types of damage and all that bad stuff. Your actions:
Couldn't you use a thief detect illusion ability to drastically shorten this process?