What do you mean "if" he starts shooting?? You seem convinced that he will no matter what.
That's a mighty small "if", and an even smaller chance that he'd pick me to be his target out of a bunch of people in a restaurant, especially since I'm not antagonizing him. But if I stand up and open fire, I've pretty much assured myself of being his first target in the unlikely chance that I'm (or anyone else in spite of their delusions to the contrary) not able to drop him on the spot.
Ever wonder why bank branches no longer have armed guards like they did back in the day?? Because it was found that guards pulling their guns out and trying to stop the robberies actually created far more casualties than having no guard at all. It's also why every bank in the country has a "no resistance" policy for their employees when a robbery occurs. Bank employees are trained to remain calm and hand over the money. You'd have to go back nearly 5 years and 20,000+ bank robberies to find one where a customer or employee was killed. There's a lesson to be learned there. Like I said, pulling out my gun and shooting will always be an option, but one of last resort.