I'm on my work phone and haven't watched the video. If its the one I'm thinking of the attacker is a monster sized convicted felon. 7 guys might be enough to take him down, but how do you know the other six are going to jump in?)
I'd tell someone to call 911, back up and draw. I'd tell the guy to get off the victim, and if I thought the victims would be killed, and I had a clear shot without endangering others, I'd do what I had to do. It's clearly a disparity of force. If he stopped the attack on the victim and attacked me, again, I'd do what I had to do.