If one of your Sims dies, sell everything in the house. Then, evict the family and buy the house again. When the house loads, all of the Sims will be alive with full mood bars.
In order for this trick to work you must have one other Sim in the house. When one of your Sims dies, the Grim Reaper will appear to burn it to ashes. Use one of the Sims to plea for mercy when he is near the dead Sim. You will then play rock, paper , scissors with him. If you win he will make the dead Sim a zombie. If you lose he will burn the other Sim to ashes. However if he is feeling generous he will make the dead Sim a zombie. If the Sim becomes a zombie and you do not want it to be one, to get the original Sim back enable the move_objects on code. Delete the zombie Sim and select its face again in live mode. Your Sim is now back to life.
When a pet or a person dies, enable the move_objects on code. Delete the Grim Reaper before he can get to the person or animal. Proceed to delete the person pr animal. Click their head in the panel and they will reappear. They will be alive and well.