Death is usually the endpoint for me. Although some have been known to stick around for a while afterwards.
Seriously though, just because I play with aging off doesn't mean my Sims don't age. I just age them manually with cake. That way I have time to play out my story to my satisfaction. (Nina has a fight with Dina over her criminal career and moves to a grungy apartment in the city. Disgusted by her new lifestyle, it is easy for Nancy to persuade her to work as a part time maid while living amidst luxury. But then she makes a deal with Geoffrey...)
Since I play in rotation, I play until I feel a chapter is finished in that household's life. Then I make note of whatever age I think the Sims have reached during that chapter with maybe a brief reminder of what I want to do next time.
