Lich with a combined spellbook class is absolutely, totally nuts. I'm in late Act 5 finally, and I just blow shit up with my 20 wiz/Mythic 9 Lich. Most major bosses don't last more than 3 rounds in turn-based mode when I'm hitting for 450+ on a cast of Negative Eruption.
My companions are basically just cheerleaders now, with the exceptions of Arueshalae and Kestoglyr. Kestoglyr is surprisingly great- a late game Lich-only companion you get to customize almost from the ground up (he starts with 3 levels of fighter, dual-wield scimitars). He has very little dialogue/special interactions with anything, but - after I turned him into a 10 Primalist Bloodrager/6 Fighter/4 Dragon Disciple build I found - I stopped caring. Who needs to talk when he's throwing out 13 attacks (plus making them shaken and flat-footed) on every charge?
Also: if you're playing as a Lich, the Repurpose/Flay for Purpose spells are "I win" buttons for much of Act 4-5. This is really true in the demon city, where you can Repurpose powerful demons and, after you kill them, they become a near-permanent summoned pet in that part of the city. Balors are especially good for this, as they're very tanky and don't have much in the way of good loot (usually just a +1 longsword), so you don't miss out by Repurposing them. By the end of Act 4, I had 3-5 high level demons waiting to follow me in all 3 tiers of the city, so any encounters ended very quickly in my favor.
