Perhaps, especially if the customers had been combat trained/experienced. However, I recently had some very realistic training in how to respond to a situation like this and it is incredibly hard to overcome the freeze response. I read of one survivor who said something like, "My heart was pounding but my body was stuck."
OTOH, Shaw did just what our trainer recommended - even for kids in a classroom at a school shooting: rush the perp. The only "training" most of these perps have had is playing video games. Making noise, throwing things, rushing him is going to distract/disorient him. You have a much better chance of survival than the duck & cover strategy. But it does mean overcoming the basic mammalian freeze response.
The new rules for dealing with an active shooter is, Run, Hide, Fight.
Most incidents are over in seconds. You have a choice. Make it.