Vigilantes will begin to do “Death Wish” armed “victim bait” walks. Stroll through the same areas looking vulnerable, but with the hand on a concealed pistol.
It's just a matter of time. NYC and Philly used to have extremely effective “stakeout squads” consisting of gung-ho police marksmen. They would stakeout shops that had been repeatedly robbed, and slay the armed robbers who arrived for “business as usual.”
The bleeding hearts had the units disbanded. Too effective. Not nice. “Stakeout squads” had to be banned.
But armed vigilantes will eventually do what the police will not do, if it is the only way to frighten these beasts into better behavior via the fear of sudden death.
While it’s not a hard and fast thing, I do note that most of these events seem to have been in places without much in the way of concealed carry.