Lets say my person is level 9 chef career, I left my game unattended, I had one baby and I am playing on the epic lifespan. Well, when I left my game unattended on slow speed while I made dinner, and when I came back my girl was in labor, I was like oh no, well I can handle two babies. Well She had three so now they have four babies, and the oldest baby won't age into toddler for another 17 days. I really would like to see about quitting the job, but I want my person to be able to come back to it. If she quit, is it like the other sims that you can just come back to the job at the same position or would she have to start from the bottom all over again?
Similarly I got to level 10 (master thief) in the criminal track then quit and immediatly rejoined because I wanted to unlock the evil track uniforms (problems there but that's another topic) and started at Bagwoman (level 5) rather than decoy (level 1). So I'd say if you quit and rejoin you start over in the middle not at your old level but not at the begining either.