It's funny you ask, I actually just posted about this in a separate thread haha, I can copy/paste:
Ghosts in households (including non-active and NPC households) that live in the worlds will generate tombstones upon their death, including when you are not on the lot and they die. Ghosts/Tombstones now have their own culling timer as well, that when going below a threshold the tombstone gets a new interaction called 'Strengthen Connection to the Physical World' which resets the culling timer for that Sim.
This way the user can control what dead Sims they want to keep around while letting others expire on their own. And when they expire they get sent to the netherworld and are culled.
