I will do exactly as the cowboy did, retreat have some distance when the BG are busy looting the Register, Draw and double tap each at very close targets 1 and 2 are very close to each other. The 3rd BG, when under fire, will most probably flee or not he will receive the rest of my 12 rd before I have to reload. I Should not hit the lady at 7 yrds if did happen than I have to live by my actions. She may freak out and get into confusion of the gun fire. I assume armed robbery could end in killing all witnesses.
One thing I may do is to grab the lady and retreat together and clear her out of the line of fire, since I most probably I would be engaging in a shoot out.
The only advantage I can see, how cool I would be when threatened by 3 raged BGs. I assume I will turn into auto pilot and terminate existing threats.
Note: this is a very good training video for handgun defense course.