I completely agree with getting out of Dodge unless you or a family member is the next target or you have the opportunity for a shot that's nearly impossible to miss.
In the El Paso situation, the shooter passed people in the parking lot while openly carrying his rifle. That's unusual enough to get my attention but wouldn't justify evasive or defensive action. That he was wearing ear protection (and, I suspect, eye protection) would, in my mind, raise the threat level to nearly, but not quite, imminent. His targets were Hispanic. Therefore, he would have had no interest in an OFWG like me. It would have been easy for me to follow him quietly at a distance of a few feet showing no sign of interest or preparation for defensive action. If he does nothing, neither do I. No harm, no foul. If police or armed security challenge him, I back out. However, as soon as he clearly shows his intention, draw and open fire on him. Then, holster, conceal and call 911 to report a shooter down and request police and ambulance. Although it would be cruel to his first victim, I would prefer him to get at least one shot off so that there could be no question about overreaction on my part. The El Paso situation was probably unique which means this won't work generally.