I disagree the guy got the drop on all of them... big time. They needed situational awareness as much as they needed a gun. If there was another person there that was actually paying attention he probably could have stopped the guy or at least limited damage.
Also nobody wants to hear this, but "shit happens. " You cannot live your life being in the red all the time. If I had to do that I'd probably not want to be living. On a probability chart of "ways some bad guy is going to kill you" what happened to them was pretty much the shit version of powerball. Even if they knew this guy was ****ed up when he got fired what are they going to do, run around waiting for the attack that might never come? In my entire career I've encountered like 4 people that would fall into the "****ing weirdo" category but even knowing they're weirdos you don't really know whether or not they're going to be violent. And in any large organization you often don't know who they would attack even if they are violent. Lots of these weirdos are pretty nebulous people.
-Mike