Hi
@peach. I'm still around sometimes!
So here is a big discovery I made in my own current (lol) dynasties: story progression will not move out the boss or coworkers of anyone in your active household and therefore, anyone in their household. I can confirm it for any full-time rabbithole job, and it might be true for kids in school (classmates use a similar logic to coworkers). My first step when I loaded up Moonlight Falls, which seems to have a mass exodus in the first week, was to fill my household with useful people, and get different rabbithole jobs for all of them, especially if an original townie I wanted to keep was part of it. As long as you keep the job, it doesn't matter if you're always taking unpaid vacation, on wedding or maternity leave, whatever.
Since I've been stuck on the end of Generation One since we were still panicking about toilet paper in 2020, I don't know my plan for the future. It's gonna happen and I think I know what to do but this is where we spin out into conjecture. Having immortals stay in their jobs or get new jobs is a good way to keep them out of your hair. In past dynasties, I was lucky with few to no families moving out, and I noticed that as the residential population thins out, there's a smaller pool of potential bosses and coworkers to choose from, and every household you care about will have a better chance of being represented.
Also what I found useful was
this guide on Mod The Sims about populating worlds in Create A World. Most of it is irrelevant to this conversation but there is a table showing the minimum and maximum number of coworkers your sims' jobs will generate. On that note, think about which jobs are already assigned when you load a town. Only Twinbrook will have original townies start in the Education career, only Bridgeport will have original townies that start in Film, and no one starts as a Fortune Teller in Moonlight Falls (crazy right?) And story progression doesn't assign random jobs that well. It basically just fills up what's relevant to your played sims.
This doesn't apply to the Immortal Dynasty at all but I figured I would end with it: story progression will not touch sims who used to live in your household after they move out.