Stan Hampson had complained that his father Stanley Hampson was "starving" because he had difficulty swallowing.
However, doctors at Aintree Hospital in Liverpool said fitting a feeding tube would hurt not benefit the 86-year-old, and a judge at the Court of Protection ruled in favour of the hospital.
Mr Hampson died on Wednesday, a day after the hearing, his son confirmed.
Doctors had asked the court to make a ruling, insisting that fitting a feeding tube would be unethical because it would not help Mr Hampson, who is fed via intravenous fluids.
Mrs Justice Roberts ruled in favour of Aintree University Hospitals NHS Foundation Trust at the public hearing in London.
The Court of Protection considers cases involving vulnerable people who lack the mental capacity to make decisions.
A dementia patient at the centre of a legal battle after doctors refused to feed him through a tube has died.