Niki Lauda's surgeon says it has been "clear for some time" that the F1 legend would not recover.
Lauda, who had a lung transplant last year, died this week at the age of 70.
The tributes have been almost unprecedented.
"The idea of not seeing his red cap in the paddock again changes everything," said fellow Austrian Gerhard Berger.
There is talk that Mercedes, where Lauda was the team chairman, will tweak the livery of its car this weekend in Monaco as a tribute.
"The news will overshadow the weekend in Monaco," predicted Ralf Schumacher.
"For Lewis Hamilton, who had a very close relationship with him, this will probably be a difficult weekend. But Niki would have been the first to say 'Keep going!'" Schumacher told Sky Deutschland.
While sections of the media have been anticipating Lauda's return to the paddock this year, others said they knew the triple world champion was gravely ill.
"His death did not surprise us," said Walter Klepetko, who performed the lung transplant on Lauda last year. "It was apparent since the beginning of the year.
"The Christmas holiday in Ibiza did him good, but then came the flu infection. In recent weeks, there have been clear steps backwards," he told ORF television.
Klepetko also told Bild newspaper: "There is no cause of death. It was a long process in the end involving a clear decision from everyone.
"At some point, you have to let go.
"I will not go into detail, as that is the family's responsibility."
But Lauda had two kidney transplants in the past as well as the recent lung transplant and influenza. In the end, he was reportedly on dialysis and a respirator.
"He was in a hopeless situation at one time, and miraculously came out of it. It was a brave and strong fight, but unfortunately he did not regain his old strength and fell asleep peacefully with his family," Klepetko said.