Take the shot. If you have the ability. All of this speculation on what will happen is immaterial. The odds are just as good that the BG will not be able to complete his action as he will.
The reason that police don't shoot is because they control the situation. They set up perimeters, control access and communication. When was the last time you heard of a PD letting a hostage taker get away with a hostage?
As a civilian, you don't have the ability to control the situation other than to take the shot. The people I have seen shot IRL (all w/handguns), dropped like a sack of potatoes. The odds are in your favor that taking the shot will end the situation. They are not in your favor that the hostage taker will spare the hostage's life.