Unless I was directly assaulted or a bystander was hurt or the subject(s) made a hostile move, I'd keep my concealed weapon(s) secured.
What's the difference between a bystander and the manager?
I'd have to try to help. You can't just stand there while someones being beaten. I wouldn't like it, and I'd expect to be arrested, but a mans gotta do what a mans gotta do. What kind of man would I be to not help?