That's a hard question to answer correctly. Different strokes for different folks. Self preservation is generally the first instinct. Bravely or cowardly. Hide or attack back. It's just based on your position, mentally, physcially, and spiritually.
If thats a mugger, I'll gladly give em all my stuff so that he goes away and then I'll report to the police. However if its a madman, I don't really know what I'd do, most likely I'll dive for his legs, try to take him down and get the gun away from him. Or if I have my metal club or dagger in posession I'll make use of them as soon as I get him down or get him in my range. If I'm far however, I'll look for a place to hide, and... crawl/roll my way there, running is useless, you'll get shot 90% of the time. Btw those tips are a must read, and thanks for sharing em. IT
I liked the part about several civilians can take him out. With a little time, I'd get the call into 911, check to see who might have mace or a tazer (or Coke and Mentos), and organize the charge - "Let's roll". I always thought throwing stuff as you charge him would easily increase survival chances by 50%. Rolling towards him probably wouldn't help you or the rest of the victims, running or jumping at him might have a corpse landing on him which would help those remaining. The big question is, are you ready to die? You never know when your time will come so you need to be ready.