Resurrect the dead or reverse death, anyone?

Well, go to his father's home. There find his gravestone/urn and wait for his ghost to come out. Build the relationship until it's nearly maxed out. You can also enable testingcheats and shift-click on his grave/urn and choose Add to Household.
There are three ways to resurrect a sim (two in your case).
1) You can get a death flower, the Potion of Youth, and anglefish and have sim who has mastered gourmet cooking skill make an Ambrosia. This food will resurrect dead sims and reset living sim's aging bar.
2) By completing Bestselling Author aspiration, you can write an epic saga where you can capture living sim's life in. Once that sim dies, you can use it to summon their ghost and once in the household the ghost can use it to restore their own life.
3) If you have Romantic Garden stuff pack, you can have a ghost wish for life from the wishing well. Positive outcome can give your sim either one of the ingredients of ambrosia or a ready-made ambrosia. Overwhelmingly positive outcome will resurrect your sim and grant them immunity from unnatural death so they can only die by old age.

@EgonVM that is very helpful, thank you. I will have to try that when I get home.