I would so love a working career where you start out as a graveyard caretaker, working your way up, caretaker -> burial ceremony handler -> graveyard manager -> graveyard master and eventually getting noticed by a supernatural entity, becoming an assistant for his trainees -> becoming a trainee -> finally becoming a Reaper. On the highest level of this career, your Sim will be granted immortality as long as they hold said position. Just because Grim has all the time in the world to train new recruits, doesn't mean he likes losing hardworking colleagues.
I'm unsure if the laws of Grim would allow your Sim to handle deaths in the family, maybe your Sim would have the option to call in a favor from Grim when he shows up, giving your Sim one week extra, but then Grim *will* do his job. Or my preferred option, your Grim Sim can call a heavenly elevator, that will take said Sim to his or her rightful place. I don't need to tell you where an evil Sim could send that elevator, will I?
There's so much a pack like this could give us both in career, b/b, Occult lifestate and CAS, I don't have the energy to write it all down. Lots and lots of spiritual things, an altar with various blessings for a Sim and torn-up clothes fit for a zombie.
EDIT: While I like the ideas of zombies, I don't want the game to spawn them like it does with the other Occults. Zombies should be created and handled by the players only. Perhaps an event where a neighbour is risking a zombie spawn, and you'd have to call some professionals to handle said matter.