Please Save my Sim!?! [I got super lucky]

You can save your sim to your own library while you are still working on them, as long as you give them a name and traits (you can still change their traits after that as long as you don't exit). I do this all the time. If the game crashes while still in CAS, I can grab the sim from my library when I restart and continue working on them. I have also used this when I didn't have time to finish working them (needing to go do chores or go to work etc.) And I always save the completed household to my library independently before I do the "save and exit" just in case something goes wrong. If you don't want the incomplete or extra copies in your library, you can just delete them later.

EDIT - JUst realized that @MrPlumbob also mentioned this. I should have read more carefully. :lol: But this really does work. Just periodically save your household to your own library, and then later when you are done and they are safely in their home, you can delete the unfinished versions and just keep the most recent as backup.