This one has always sounded like one of the toughest scenario's to deal with.

A rush of multiple armed attackers intent on robbing everyone in the place. (or ?)

Some factors:

-Sitting where you can see the entrance / approach?
-Cover / concealment available?
-Exits
-Bystanders
-The people you are with, if any
-Flee, Fight, or try to comply?
-How many bad guys? All armed? Chance of "undercover" bad guys?
-Backstop?
-Suitability / capability of your weapon?

Thoughts?