So here we go. Only pre-buffs required is a Chain Contingency or Trigger, centered on self consisting of Mirror Image + Improved Invisibility + True Sight. Fire that upon sight, then wait for the lich's scripted Horrid Wilting to pass. I find that it tends to disrupt spells of slightly longer duration (like Time Stop) if you start casting them too quick and the Horrid Wilting catches you.
Summon some fodder [w/ wand preferably] to distract lichie, then move back a little. Project Image if you don't want to waste lvl7 and above spells, and Time Stop ASAP. It's important to try and do this before the lichie casts Time Stop, because he will most probably cast Improved Invisibility again which might make him untargettable (it takes some time for True Sight to dispel it). In other words, make sure he is visible before you cast Time Stop in any case.
Once you've stopped time, immediately cast Improved Alacrity. With Vecna & Amulet it allows you to truly "unleash hell" during your Time Stop. Follow with Spell Immunity: Abjuration if you like, just to be safe [Lichies likes to cast a Remove Magic + Chain Lightning + Chaos trigger at a (closest?) non-fodder character]. Next, the goodies: Ruby Ray, Khelben's and Power Word: Blind. This is guaranteed to be extremely annoying to the lich. Next, set up 3 Delay Blast Fireballs in a Chain Contingency targeting nearest enemy on condition: see enemy, then move slightly towards lichie so that the contingency activates (still in time stop, mind you). Delay Blast Fireballs seem to take some time to cast, so casting them through Chain Contingency guarantees speed. Use the remaining Time Stop period to stack Inc. Clouds centered on a point slightly behind lich (so you don't damage yourself) and then move back.
Lich will be blinded, stripped of all his spell protections, hit with some heavy fire and right in the middle of a raging fire storm probably wondering what in the world just happened.
Now, I've given up trying to use Horrid Wilting to kill those improved liches, it doesn't work well. Instead, this recipe should be able to take care of liches pretty fast. No waiting around for Prot. from Magical Weapons to wear off, no worrying about being level drained or imprisoned while you're smacking the lich with melee weapons; you shouldn't take damage anyway, unless that first Horrid Wilting hits you.
If you don't have a sorc, this recipe will probably be hard to execute. However, it is vital to have someone cast True Sight, Ruby Ray & Khelben's (superior than Spell Strike IMHO, because of the delayed effect of the latter), then blind the lich with Power Word: Blind and try to cast at least one Inc. Cloud at him. If you don't have Inc. Cloud, or don't want to cast it, you can keep summoning fodder at the blinded lich and look on as he imprisons, stuns, spell strikes them to death. Wait for his Fireshields to wear off, then move in with 2-3 melee characters and kill him off in seconds.
Alternatively, summon 6 or 7 planetars through Project Image and send them at lichie. He will imprison maybe 1 or 2, stun maybe 1 or 2 but will surely fail a death save and be destroyed by the planetars' vorpal weapons. Too cheesy, but I did try it out.
