If you have Get To Work, a high level Scientist, and enough lifetime rewards, you can have a pretty much immortal sim. Just make a cloning machine and a potion of youth, and clone that potion a bunch and hey presto!
Also works for death flowers and other potions if you want to be TRULY immortal. My scientist doesn't sleep anymore, she can catch on fire or electrocute herself as much as she likes and puts herself in whatever mood she wants because of her endless supplies of Youth Potions, death flowers, sleep replacements and mood potions.