Anyone who doesn't want to be overtly spoiled about the Caslte Ravenloft module, stop reading right now.
....
Alright, that's enough warning.
Here's the deal. My group has kicked the shit out of Strahd. However, they did so without consecrating the fanes, or defeating all of the powerful NPC's. They want to continue, so I took the two most powerful NPC's and have them fight over Barovia now.
The Necromancer: She was actually killed by the PCs, but they left the body there for three game-days without touching it. My rule is any corpse that lies unattended for more than 5 minutes is the DM's property. So, I brought her back as a templated Morhg. I also ruled that the crossover to undeath was extreme enough to warrant a rebuild, and I rebuilt her as a necromancer that doesn't break the laws of physics by sucking and blowing at the same time. (She is now a single-classed uttercold assault necromancer.) She rules the lower part of the castle, and has a strong defense around the Dayheart until she can figure out a way to move it.
Khyristryx: The players fought her once, but she was driven off (She wasn't defending the devil trees at the time, long story). She survived, and is now lording over the upper parts of the castle. I also changed her a bit, I kept the changed up SLA's, but I exchanged some of her hit dice for warlock levels.
In both cases, their CR has been upped using the rules in Exemplars of Evil for increasing the levels of recurring villains.
I then divided up the NPCs. Anyone undead is now under control of the Necromancer whether they want to be or not, and the living contingent of Strahd's minions are serving Khyristryx.
Right now in the game, The Necromancer is winning. She has bound herself to the swamp and mountain fanes, and the land of Barovia has been twisted as a result. (Strahd was a right prick, don't get me wrong. But he still had a use for the living, even if it was to feed from. The Necromancer just wants to reduce the world to ashes, and as a result Barovia has become a worse place.)
The only remaining point of light in the area is the Forest Fane, where Madam Eva and the Vistani are holed up at the moment.
Anyway, I am brainstorming legitimately unsettling encounters to throw at the players to represent that Barovia is now much, much worse for the wear after killing Strahd. I'm currently ganking stuff from Heroes of Horror, but that will run out eventually.
So far, the only line that I won't cross is rape. I don't like to even have sex in my game if I can possibly avoid it, I'm not going to have any rape themes in the game. Laugh at me if you must, I don't care.
I'm going for more of a Silent-Hill type horror, rather than 80's slasher movie theme as well.