Sim died, but why was she deleted from the game?

It sounds like sim culling to me. I don’t know enough about it to explain very well, but I’ve seen the subject come up. It doesn’t seem to matter what your sim count is because the game has a limit on how many of your sims plus other sims it can handle (I don’t know the number, sorry). If you’re playing a save from 2014 my guess is that you have a lot of sims in it. Maybe if you delete some nobodies you can prevent future culling?