None of my sims has died since I started playing Sims4 last spring - hold on, one may have been killed in a kitchen fire. I quit without saving and didn't care that I'd lost over 2 hours of gaming. Also, I did kill off a few townies...
Back in my Sims 1 and 2 days, if a sim I really loved died unexpectedly, I'd stop the game and exit without saving. My favorites are not allowed to die. I play with aging off.
I would also stop and restart for other sims, but if a sim really seemed determined to die then I'd let them go, call them an id.iot, and continue on with that family. I had one house in Sims2 that I swear was cursed, the adults kept dying in stupid ways and no matter what I did, they'd just keep doing the same things and dying as a result. I restarted at least 3 times when the mother died of hunger (toddler and baby in the house - those kids'll get you every time). The rest of the family kept getting in front of the fridge, preventing her from getting food. I tried moving the fridge and even putting food in front of her and her family kept getting in the way. I gave up. Later the father went swimming. The rotten kids kept getting in front of the ladders, preventing his leaving the pool. I tried at least 4 times, telling the kids to go away - then the neighbor got in the pool... I finally gave up when he died again and the game told me the game was over because there were no adults left. I finally gave up on that family and deleted the House of Doom. I didn't build on that lot again!