Can you restore a backup from before you lost the business? My guess is the ownership was tied to the household, and since you moved him in with his parents instead of his parents with him it essentially deleted his household when he merged into theirs. If you can restore a backup of the save, try moving the parents in with him, then moving the whole household to the parents' old house.
@PipMenace @dinastrautmane Yes, if memory serves, any owned business is attached to the household that it was purchased through/with. If someone moves out of the household, the business stays with the household they moved out of.
When I've inadvertently lost a business I've repurchased it successfully. So if you have the funds that's an option.
It should still exist in the game but as an unowned business, that's how it's always worked for me.
If there was someone left behind in the previous household who now owns the business, they would just have to sell it first. Technically you could move your Sim back and take the funds from the business sale, move back to the parent's house and then buy your business back.
