All perfect praise be to Allaah, The Lord of the worlds. I testify that there is none worthy of worship except Allaah and that Muhammad is His slave and Messenger.
Contemporary scholars hold different views regarding brain death and whether the brain-dead patient is legislatively declared dead or alive.
Shaykh Ibn Baaz was asked, "What is your opinion about doctors' claims that a brain-dead patient is actually dead?"
He answered, "This claim is not reliable and has no evidence to support it, nor should it be acted upon. I was informed that some patients who were declared brain dead regained life and resumed living. Consequently, being brain dead is not considered terminal, and a person suffering such a condition is not considered to be dead until his death is certain."
It is impermissible for the woman to remarry another man unless her husband's death is confirmed and her ʻiddah (waiting period) expires. If the husband's death is merely doubted, then the basic principle is that he is alive. The famous Fiqh principle reads, "Certainty is not overruled by doubt."
Allaah knows best.