Tier 1: Harvest Life should be baseline and replace Drain Life, with perhaps a destruction variant. I wouldn't mind having a cast and channel heal on a low cooldown (like pre-MOP Soul Harvest but with a cast time as well) to replace it.
Tier 2: Alright, but honestly I don't think Mortal Coil should have the heal (I know, a "nerf" but it could be balanced around by say, more siphon/drain healing). It feels too mandatory to take a personal versus CC.
Tier 3: This tier seems OK for now.
Tier 4: Could use a lot of work; I don't even know where to begin.
Tier 5: Seems alright to me. Personally I would love if you got Lesser Invisibility by sacrificing a succubus. The stealth would be incredible, plus a new curveball for RBG's (at the cost of an interrupt). Stealthed warlocks? Yes please.