Dead is dead. You can't heal dead, at least at this point in our medical abilities.
But a vegetative state is not necessarily "dead".
My mom was "out of it" for almost a year. Mostly non-responsive, seeing imaginary things, did not know her family. Doctors said that was it, they never recover,
One day, bing, she came out of it. She was fine. Rational, coherent, knew who we were. Lived another 10 years and died in her sleep.
The doctors were wrong.