Nope. I pretty much assume that everyone kills these days no matter what you do. I had an incident some years ago where a man tried to assault me at a payphone. I fought back not knowing if he had a knife, a gun, or whatever and he left. Then I called the police with a good description of the perp.
But in this situation it was an unarmed room of young people and women, and the perp was a guy with a shotgun and a semi-auto handgun. The only thing that you would accomplish by trying to attack him would be forcing him to shoot.
Also, it may be one thing to make that decision to defend yourself, but in this situation, an attempt to defend could result in the guy shooting others.