When I get bored by a certain family or feel their story has run it's course, I usually start a new family within my save. I like encountering my own sims in my save. There are sims I switch back to when I feel like it.
I would only give up that save if it becomes totally unplayable. Let's hope that doesn't happen.
If you start new games in the same save, how do you keep it safe from bugs and corruption?
I hope I can avoid corruption by limiting mods, no big mods with overhauls or new systems , regularly save as, no rental units. But it's all down to luck. One house has a lot of lag so I might have to move the families I care about to a new save at some point.
I play a lot of rotational. It is not uncommon for some bugs to be house-specific. Like one of my beach lots, constantly bugged with people swimming through the floors and students coming home mid-school day. If I travel with a parent and then return home before the kids are supposed to be home (I had to finally move the household out and back in to fix that one). It is like the lot itself becomes the cause of the bug. It was also hit-or-miss which household was affected by the black photo bug until the January bug hit them all, so I played for the first 48 hours after the update.
Weirdly enough, some bugs resolve just by switching households and then switching back. Also, some of the smaller bugs and glitches can be at least temporarily fixed by going to manage worlds and right back into the active family. I just had to do this to get a completed formative moment to actually disappear from the list so I could pick a new one.
