If a person has completely become brain dead then there's no chance of recovery and there's no way for the completely brain dead person to survive without the use of life support.
So if someone has become brain dead and cannot recover then the best thing to do is take the brain dead person off life support.
The brain is what keeps a human going and controls our bodies and without the brain being alive we cannot move, talk, walk, etc.
Even if the body continued to live while brain dead the person would not really be alive anyway because they would just be lying there.
If only some brain cells die then a person can usually recover but once the brain completely dies then sadly there's no chance of the person recovering once they are brain dead.