Under those circumstances no one knows for certain what they would have done other than follow their training.
What he said. In any case, having considered the situation or as many situations as you can prior to them arising, i.e. getting yourself and loved ones out of the line of fire, the serious risk of doing harm with stray bullets when a measured controlled response is not possible, or 2+2 if it is a viable option, thinking it through ahead of time puts you in a better position than the average citizen, and more likely to be among the ones that walk away rather than get carried away. Threads like these that run your mind through the "what-ifs" are a form of preparedness. As you're out in public, take a look around, be aware of your surroundings so that if the bad people come, or the kitchen in the restaurant catches fire, or there's a storm, or .... fill in the blank, you know your escape routes, how many rounds you have in your CC and the distance that you can put 2/2 in a 4" circle, and the other things that you can accomplish by an inquisitive attitude and solid observation skills. All of these will stand you in good stead regardless of the circumstances.
I'm CPR certified, and I also served my country for 20 years because of all the books I read growing up about our heritage and the results of action by citizen-soldiers that formed our country. If I see someone choking etc. I feel a duty to act. If the Flight 93, or Aurora, or or a Virginia Tech, etc. situation developed and I was CC, I would feel a similar duty to act. Life is precious, and worth protecting. First of all, do no harm.... By which I mean don't make the situation worse. If you can act to make it better, act with the least amount of force that will correct the situation, but act decisively.
We do not rise to the level of our expectations, we fall to the level of our training. --Archilocus, 650 B.C

