Gosh, we used to have random deaths quite often back in Sims2. Gave a certain edginess to the game, I always thought. A challenge to keep my
Sims alive. I made certain to set the this new introduction into the game to protect my active families. Once the YAs move out and onto Uni, I will set their parents' household to allow Dad to retire, but I have allowed NPCs to have whatever the game throws at them. I am in the habit of creating and playing, only, my own Sims, though. I'm so sorry for your loss. Can you roll back a save or two to try to prevent the death?