first of all i am very sorry that your father met with such an accident. first let me tell you some facts. head injuries are very unpredictable. no one can tell you about the recovery time. it can be hours to days to months to years and sometimes life long coma
. since decompression surgery is already done now nothing more to be done. just normal nursing care is needed. try to keep him clean and dry. have a water bed to prevent from bed sores. rotate him once in 2 to 3 hours.. try to listen him some music . because it will help in fast recovery.
wish your father with fast recovery