Hello Ms Reeta,
Probably the brain damage
following the head injury
was too much and so your father has not recovered. Unconsciousness
for 20 days following a injury is very long and indicates poor chances of functional recovery. The doctor must have assessed the brain functions by means of examination before communicating to you that it is not functioning properly. The decision to take him home remains with you. There are no medications which can really improve brain function in such situations. Any recovery that occurs is due to the healing of the injury to the brain on its own.
Nursing care is most important in such condition.