Somewhat sorta, kinda.
The first rule of a gunfight (even if you don't have a gun) is MOVE! Moving targets are an order of magnitude harder to hit and this guy wasn't using aimed fire apparently. Don't stand around and try to determine where the bullets are coming from. Move.
The second rule is move to cover. This is harder because cover is loosely defined as a barrier which stops the bullets. What is cover from a 9mm pistol is not always cover against a .308 rifle, for instance. The corollary is that if cover isn't available, move to concealment. Concealment is a visual barrier which hides you and therefore makes it harder to be deliberately targeted.
The third rule is to return fire as quickly as possible, preferably while moving to cover or concealment. As a general rule no one wants to be shot and having your target shoot back creates a non-zero chance of you being shot, even if he's moving (to cover) while shooting at you. Most people understand that when your target is shooting back that they should hunker down. This usually means ceasing fire, reduced fire, and/or less accurate fire.
The fourth rule is to be the first to put accurate shots on target. This is hard to do but if you can put shots on the target, your chances of winning go way up. The more accurate the shots (to vital areas) the more your chances go up. The more quickly you put shots on target, the more your odds go up. While an attacker might be able to continue to attack you after he's been injured, he also might not, however, not being injured ensures that he is still capable of continuing to attack you. This rule is often (slightly erroneously) summarized as "The first person to put shots on target usually wins."
To be specific to this horrible event (may the murderer's soul be tortured for eternity), the recommendations are to MOVE to cover; walls, indoors, brick walls, hiding, etc. I do not believe it very likely that it would have been a great benefit to stopping the shooting had anyone in the victim zone been armed, even with a rifle. The murderer was active, according to official police timelines, for 11 minutes. It is not easy for people trained to it to track down the source of fire at that distance, hight, and location, deploy their weapon, and return fire. Particularly if it is not a two-person team with one acting as a "spotter." A few minutes of confusion followed by the team trying to find a good place to setup for fire, then tracking down the exact location as well as the requirement for much better accuracy than the murderer.
What made this murderer stop was apparently his discovery by the hotel security guard. Once he shot the guard, it appears that he stopped and likely committed suicide soon after. LEO was on the floor and in position in 11-12 minutes. I did not believe this at first. Heck it takes 8 minutes to climb the stairs to get the right floor. However, it has come out that a 8+ man police team was, by pure coincidence, right there on site and responded immediately (good training there!). But it was still well over an hour before LEO breached the room.
That said, if you are armed and do have sufficient training and practice, making difficult shots at distance, even with a pistol, is not only possible but has been done, as shown when Airman Andy Brown (AF Security Police) stopped the mass murderer at Fairchild AFB Hospital with a shoulder shot and a head shot from 70 YARDS using is issue Beretta M9 9mm pistol.
So would it have stopped sooner had any in the victim zone shot back? Probably not, but there is evidence to support a solid "maybe."
My bet? Move to cover.
Peace favor your sword,
Kirk
