My son passed 20 months while he was sleeping. Few hours after he came from drinking for about six hours after his scheduled hours at work

There is a cause of action against a bar if they negligently "over serve" someone who is visibly intoxicated, and then that person goes out and injures someone else while driving, or injures themselves.  It is known as the "Dram shop" law.  Whether or not the bar has liability will depend on very specific facts such as the blood alcohol level, the length of time he was drinking, etc.  It seems from the information you provided your son worked at the bar, so there could be a worker's compensation portion also.