My 2 cents - the CHL instructor chose to involve himself in an incident in which he was not a part of, chose to escalate the situation by following the deceased from the store, chose not to walk away from a situation that could only get worse by staying engaged. Had he walked away it is unlikely that there would be loss of life. Now he has to live with taking a life and deal with any potential wrongful death lawsuits from the deceased's family.
When dealing with belligerent drunks the best thing you can do is distance yourself from them. IMHO, the proper tactic for the CHL instructor would have been to walk outside and call 911 as soon as he determined there was a reason for police to respond.
On a side note: Many, many years ago I worked at a 7-11. As part of training management made it clear that there was nothing in the store worth dying for, so if someone wants to take anything let them have it and leave the property without escalating.
NRA Life Member, TSRA Member
“The consolidation of the states into one vast empire, sure to be aggressive abroad and despotic at home, will be the certain precursor of ruin which has overwhelmed all that preceded it.” Robert E. Lee