Why do you need to ask? Is there some indication that the Bronx D.A. is not going to prosecute? We need to do what we always do in a Constitutional government.
Why do you belive that the only remediation is to wait until the act...such as the one which I believed I had sufficiently outlined in the OP...took place?
I don't want this thug convicted and imprisoned after he imprisoned his victim for life! Which on will get out of their prison sooner?
So you wanted him imprisoned BEFORE he hit her?
While that would seem to be a perfect solution, don't you see something inherently wrong with it?
No, Samson, but ideally it would be appropriate to stop him before he actually delivered the blow. That CAN be done.
That said, there are a few caveats. Assuming you can carry a gun legally, you need to remember:
(1) a weapon is NOT a substitute for situational awareness. If you are not aware of a potentially developing threat around you early enough, you will not have a chance to employ your weapon. You DO NOT need to draw the weapon; you do need to have your hand on it, and be ready to draw if necessary, before a potential attacker is within kicking/striking range. Once you see a potential threat, your first priority is maintaining distance and/or a barrier(tree, wall, vehicle door, etc.) between you and the threat. If possible get away, if you can. This is a civil situation, not combat, and retreat, if possible, is a better option than engaging. NEVER, EVER, let the threat get within arm's reach.
(2) A gun, without adequate training, is worse than useless. A typical concealed carry course is NOT adequate training. A lot of practice, and competitive shooting against the clock , with realistic scenarios, to include multiple targets, is essential. Compete with whatever rig you intend to carry with, NOT a competition holster system. Your goal should be a time of under .6 seconds from a visual or audible signal to a hit on the six-inch target at 20 feet, EVERY SINGLE TIME, from your concealed carry holster, wearing normal street clothing. If you cannot or will not meet that standard, DO NOT CARRY A HANDGUN!
(3) It is a VERY bad idea to use ANY kind of weapon as a threat! If you MUST draw the weapon, you must fire when it lines up on target; at least two shots, center of mass. Hesitation is FATAL! This means, that you had better have exercised all possible precautions, and had them all fail, BEFORE you actually draw. Assuming you have, this is now the gravest extreme, and, YOU HAD BETTER NOT MISS!
( 4) A gun can save your life. It can also be a great producer of false confidence. The latter will get you dead or in prison. If you have any doubts about either your skill, or your ability to accurately size up a situation and respond appropriately, DO NOT carry a firearm! There are alternatives. In the situation described in the OP pepper spray on a keyring, or simply retreating, might have worked as well or better.
(5) There ARE alternatives, which can buy you time to get away from a mugger. A second wallet with a twenty dollar bill and some long-expired credit cards in it, makes a convenient throw down. So does a fake high-end watch, or a ring or other jewelry that looks real but isn't. Either may buy you just enough time to get out of a bad situation. In a pinch, there are a number of everyday, lawful to carry objects which can save your life. Remember, YOUR MIND IS YOUR PRIMARY WEAPON!