Then theres the CCW who figures disgression is the better part of valour, perhaps trying to get his family out of the way. He and his are fleeing a man who's shooting everyone with a Bushmaster and here comes another man with a AR blocking the exit. Possible bad news there."
Good point this is a very complex subject. The only thing i can think of is training to help minimize this. I think for these kind of things you need to have gun on hand to really help out much. By the time you go to your car and retrieve your rifle your about as good as the police that are on the way.