In one of my gameplay, my female sim was best friend with Cornelia Goth. Then, when she dies she get the Oh my Ghost opportunity and she take it and take the urn to the Science building. Then, Cornelia Goth came out in ghost form. After playing for some time, i got spooked from all the ghost noices, so i merge her with the current Goth household. Around 20 days after, my sim got a phone that Cornelia Goth will die. Instantly, my sim visits her house, stays up all the night. But nothing happens. So, I thinks without mods, ghosts can't die, but can go back to neverland by clicking their urn in their inventory.