About the only "thing" that may help in those type tragic situations is your wits, circa a fast thinking convenience store clerk in Phoenix ~1993: The bad guy walked in the store with his gun out, the cashier starts unloading the till into a bag, but feigns glances to the left of the bad guy a couple of times then says "hi officer smith". The bad guy turns all the way around to (not) see the (phantom) cop and is promptly shot in the back of head by the clerk and dies.
Yep, create you own diversion. Back many moons ago I was big into Karate, and we got taught about diversion tactics. Raise your arm up quickly at a 45 degree angle, shake your hand rapidly and scream. 99% of the people your are facing will look up at your hand. There’s your diversion! May only last half a second, but that half second may be all the time you need. If it doesn't work, at least you went down trying.