Do you mean the everfrost bear caves? Permafrost bear pits is something COMPLETELY different.
The Lich of Miragul is undead so I think invis vs undead should keep you safe. Potion of Unlife Awareness should be well within your means if you've been working on your alchemy. Otherwise I believe it just wanders through the hallways when it's up, so take care when traveling.
For other (era-appropriate) info, see here:
http://www.eqclerics.org/forums/showthread.php?t=7605