I have thought about these situations and it seems like the best plan is one of escape and defense, instead of being the hero. I would not take my gun out, unless I had to shoot.
Protecting loved ones would be my first concern. Protecting myself would be my next concern, but if the opportunity arose to take the bad guy out, to keep him from killing others, I just don't think it's in my makeup to not try to stop him. I am probably going to take him out if I can. However this is not a situation for a mouse gun, and for certain a mouse gun that can't be shot well.
But no one knows what they will do, until put to the fire. It will never go down like you might have for seen in your mind. There is hardly anything positive that is likely to happen to the person that decides to play the hero and a whole lot of bad things can develop from getting shot by the bad guy, or another good guy, or shooting a good guy yourself, to getting sued by the bad guy's family, etc. or getting mistaken by the cops for the bad guy. But knowing all of that, I just don't know if I could cower down, and watch innocent people being killed and do nothing if I had the means to stop it.