I recall reading--I forget exactly where--the mother died of natural causes in 1998; hers was the type of case people would think of when talking of removing the feding tube from terminally-ill patients: although removing the feeding tube may have hastened slightly the rate at which she died from other causes, I don't think she died of dehydration.
As for the father, he suffered IMHO from a fatal case of Felositis. I think he died in 2002, and prior to his death he had objected to Michael's treatment of Terri. Just my opinion, or 'hunch' if you will, but I suspect Michael and Felos wanted to shut him up permanently.
Floriduh Voter once posted:
"Felos's mother backed over his father in their driveway with the family car until dear old dad was dead."