There is a large number of sites - particularly fundamentalist Christian sites - claiming that the people who meet the diagnostic criteria for brain death are, nonetheless, capable of recovering.
[Japanese and German critically ill patients] are being treated with hypothermic therapy. Published results are reporting that 60 to 70 percent of patients are recovering. This is a remarkable success rate!
Patients with the same types of injuries or conditions in the USA and other countries are deliberately being hastily declared "Brain Dead" so their organs can be taken.
Real Science Radio's list of "brain dead" patients who've recovered tells shows that doctors and hospitals are sometimes dead wrong.
There were never sound scientific or philosophical grounds for a redefinition of death based on the loss of testable brain function while the body remains alive
[...]the apnoea test, which might lead to the misdiagnosis of respiratory centre failure if inadequately stimulating. If stringent, it might prove lethal
Many examples are given. When I searched for some of the names of the alleged victims, I found multiple pages of similar credibility nearly exclusively. I could find no scientific or other veracious sources.
Is a diagnosis of brain death reliable, in that the patient is not able to meaningfully recover and become conscious again?