The drinking part is a separate issue, since it sounds they all drink in the family.
It's the drinking/driving issue that is more of a concern to me.

If he or anyone was that drunk and walking the street carrying a gun what would you do?
Just leave him alone or call police?
A car can be as deadly as a gun right?
That's how I would look at the situation if it happened again.

Innocent people could get hit & killed if he tried to drive in the condition he was in.
He might have just gotten home from somewhere or was planning to go somewhere but passed out instead.