You would probably be better off selling the car to a private party. Not trying to sound cold but the dealer isn’t going to care about your dads diagnosis so they will be looking out for their best interests when negotiating the deal. If they are willing to buy the car back, it will probably be for less than the car is worth. So keep that in mind. They will want to buy at a price that allows them to turn around and sell it at a profit.
Worried in Ca is probably right however if you do not feel you are able to try to sell the car on your own I would suggest trying several dealers. I would imagine this car would be one that is desired. If you can find out the blue book value that would be helpful. My friend had to sell her husband's car after he suffered a major stroke. It was a good car without alot of mileage. She contacted several dealers and went with the higher offer which was significant.
probably be for less than the car is worth. So keep that in mind. They will want to buy at a price that allows them to turn around and sell it at a profit.