Lots of wind here, less substance. This happened about two miles from my house. The guy was still an active shooter posing an immediate threat, loaded firearm in hand after having shot three people. The two interveners were both well trained (one military, the other security) and both gave verbal commands to the shooter to disarm before firing when he either fired at them or made gestures to indicate he was about to. Here in Oklahoma the law is clear -- you may deploy deadly force in self defense or in defense of others, both of which apply here.
Sorry but I spent too many years on the street with the cops seeing the realities out there to ever get in synch with the mindset of "my gun is only for me and my immediate family and otherwise I will run away!"
No one can predict every possible situation or eventuality but in a situation like this one I would not hesitate to do what the two guys did. Had they not acted when they did there could easily have been multiple additional innocent victims. Sorry, but flight is not an option.