You could also come up with a variety of scenarios where the players keep playing even after they die. Vampires come to mind here.

Intellect Devourers or Dybbuks or something similar might also work. In a campaign I played a while back a PC got replaced by an intellect devourerer and I decided the best way to handle this was to allow the player to keep playing, just with the secret knowledge that he was now an intellect devourerer piloting his old character around. He was a spy for BBEG for a while and when it became clear one of them was a traitor things absolutely took a horror turn when I instructed the PC-turned-devourer to lock the party inside their own base and eliminate them.