@GiardiniDiMarzo and @Psychotps I have successfully used the spellcasters method on some of the Island ghosts in Sulani. Three of them are now functional Sims and appear frequently as live Sims at the bar and parties.
So @cwray0 I would suggest you train a Sim as a spellcaster and put the spellcasters household into the game save you have with the deceased Sim. Than use the rotational gameplay to revive the ghost Sim from the family that you were playing. After that split the household and create a new one with the Sim you are so fond of. Then save that household to your library as @CGrant56 suggested.
Using this method you don't have to start all over and your Sim can be used in all sorts of new games without cheating.
Have fun playing. 😉
