Drowning use to be my favorite way to kill sims, I'd make them exercise till they were too tired then make them hop into a pool and fence them in. But after I got City Living they suddenly started "forgetting" to fall asleep in the water and just treaded water forever, so I went to locking them in a small room where I lit fireworks.
Somewhere on these forums I read that the game autosaves every hour, so if you figured out how to access those autosaves (can't recall at the moment) you could go back in history an hour at a time maybe (just an untested thought).
Once I left for a movie for over two hours and thought I had paused the game but really hadn't. My sim was still alive but was really miserable, just about all his needs in the red and the repo-gal had just let herself in. Luckily I had remembered to save just before leaving.
