You could apply the lich template to Auren Vrood. That would make him pretty deadly, so you might want to drop his Circle of Death (which he shouldn't have in the first place because his prestige class got changed - his CL should be one lower than it is).
You could use the seasage effigy, the ghost's essence and the heart to perform a ritual summoning something from beyond the stars, though this might be a too jarring change in tone for your group (Ghosts - Golems - Werewolves and in the end...a Cthulhu-like monster. What?).
You could make it a race against time - Auren Vrood is in the middle of a ritual which would make him a very powerful lich and they have to do...something, maybe kill something...to stop it. If they fail they can theoretically still fight him as a lich, I guess...
The bard...I have no idea. Countersong comes to mind as an often forgotten weapon in his arsenal, but other than that...no idea.