Yes. A coma is a very serious condition associated with head injury and a certain percentage of people do not survive, however many people do survive and even recover to a great degree. The longer the coma the less complete the recovery. Even short comas of a few days can cause long term thinking problems but with rehabilitation there is potential for improvement.
Complex question. This is a complex question with many variables, and is hard to answer without specifics. While it is possible for patients to survive comas, even after a traumatic injury such as a car accident, the cause of the coma, depth of coma, pre-morbid state of health of the individual, and severity of the injury to the brain and other organs all play a crucial role in the patient's outcome.
Depends. Survival is based on many factors including the extent of any brain injury and other injuries that have occurred. Many people can survive serious injuries and go on to have productive lives.