1. You can ask the police to do an autopsy and make a conclusion on the cause of death;

2. The possibility of murder is unlikely. From your description, it should be that the drunken person lay down and vomited into the trachea. Choking to death;

3. According to the latest provisions of the law: if a drunk person dies, the drinking companions who drank together and persuaded him to drink need to bear corresponding liability for compensation, but this requires a court decision;

4. You can request and sort out the identity information of several people who drank with your father and persuaded them to drink, and go to the local court to sue them and demand compensation for the corresponding losses.