Sims in unplayed households age up through the various stages and die. The game may assign them to certain roles like vendor or bartender as the game requires; I think it also assigns them to workplaces used in active careers (and I believe this happens only if they don't already have a job). I'm less certain whether it gives them actual standard jobs if they don't have them as this is an area I let a mod work on. Others may know more about it. If they do have jobs they won't progress in them, except that in the active careers you may find them switching roles - one day Moira Fyres might be the receptionist at the police station and the next day she's the Chief.
Played households should be left untouched by the game.
