I'd like to present a scenario for discussion.
Let's say that it WAS legal for someone to carry in that room who was NOT in his line of fire (sitting at the table in front of gunman). Would they still have to wait until the gunman discharge a round before they can consider themselves in harms way and return fire?
I do not believe you have to wait until a shot is fired to be in harms way. This is often a fine line of discussion but if someone is pointing a gun at your or anyone you have the right to defend yourself.