You might want to consider one other thing: if one or more perps start ordering everyone into a back room, there's a pretty high likelihood that step two will be to get everyone onto the floor, and that step three will be to start killing people.
At some point in that sequence you will lose your ability to act.
You may be well advised to seize the opportunity while you can, if it is pretty clear that the situation is really going downhill.
Yes, true. Hesitation can be deadly. The trick is in identifying that moment.