For me, my decision process will revolve around:
1. proximity to the shooter - I'm not going against a sea of human panic to try to take the guy down. However if he's close, I'll make the decision then.
2. whether or not my family is with me - getting them out of harm's way is paramount
Everything else is tertiary or "what if".
These incidents remind us that if/when the wolf shows up, the situation may be very, very far from anything we've done at the range, the IPDA match, or have brainstormed on the internet.