But seriously, what do you expect in a state that mandates by law that its citizens be unarmed victims? Even if you had a gun that you were illegally carrying in that restaurant, using it to "save the day" would likely get you a conviction for illegal gun possession.
Better to just quietly do whatever the men with guns tell you to do and hope they don't decide to kill you or your family. To expand upon a great quote from Sean Connery's character in "The Untouchables" .... "THAT's the Chicago/Kalifornia/Washington DC/New York/Massachussets way!"
To answer the OP's question, my personal decision (which is mine alone and not necessarily recommended for anyone else) is that any time a BG with a gun starts herding people into a locked room our lives are in grave danger and I will use deadly force if at all possible to avoid that situation. All depends on multiple facets of the actual scenario of course - how many gunmen? what kinds of weapons? what can I decipher from the general appearance of the gunmen - professionals? scared punk kids? meth heads? terrorists? innocent bystanders around/behind the BGs? how far do I need to shoot? in what direction? are multiple BGs spread far apart? are some out of sight? what weapon am I carrying? these are just a few of the multiple factors to consider