What happens to a Sim that dies that you haven't played as?

I made a family a long time ago, and all of my Sim's children are adults, and my Sims' husband died of old age. My Sim has an age freeze potion, so she is a young adult. I remember the Alto household, and since I used to be a Stylist, I know A LOT of people. So I kept getting these notices like, "Your Sim is mourning because of the loss of Holly Alto" etc. and I kinda just ignored it. My Sim is now an investigator, and now there is a family that lives where the Altos used to live, called the Witherspoon. What in the world happened to them? Where are there graves? I checked the mausoleum in the cemetery, and there graves weren't there. Where did they go?