Would I intervene?
Possession of a CCW doesn't allow me any more privileges or authority, and doesn't make me a law enforcement agent of any sort. However, it also doesn't make me any less of a person. So, would I (me, personally, not as generic CCW holder) intervene?
The answer is yes, I would, based on past behavior patterns and upbringing. I was raised by a Sicilian mother who would never let me live it down if I just stood by, and as a result I've stuck my nose into situations like this a time or two over the years... But I would really, really not want to draw the weapon. Given that I have never needed a weapon in the past for such a situation, I would hopefully not need it in this scenario. I don't want the legal headaches, and I'm quite happy not having to deal with any of the psychological traumas that typically accompany the taking of a life.
Frankly, the presence of the weapon complicates things. One of my major concerns would be how NOT to have to use it, followed by how to act effectively while not letting anybody else gain control of it.
Verbal warning and 911 call would be the obvious first steps. Coordination with other good samaritans, if available, would be a nice option here. Watch some reality TV whenever they show a good team of bouncers, or US Marshals, and see how often the pros opt for a one on one takedown if two or three can rush the guy instead. Help is good.
Next step, if deemed necessary, would be an attempt to physically dislodge the still conscious combatant. Ideally, it wouldn't only be me pulling the guy off the unconscious combatant. But if it were just me, unless the guy is a tank, double armbars work pretty well. So do certain chokes, but those open up a whole 'nother Pandora's box of legal and moral issues... Chokes and neck holds are inherently dangerous, and I can't recommend them to anybody who doesn't know how to apply them, or when and how to safely release them.
My mother once pulled me off of somebody by my right ear, but I don't think I'd try that approach, and I definitely can't recommend it. It was startlingly effective, though. Funny, too, even at the time.
From my limited experience in breaking up fights between humans, and somewhat more extensive experience in breaking up fights between large dogs (generally boxers, pits, dobies and shepherds - not trained fighting dogs, just out of control and excited wannabe alpha males at the dog park), it helps if you can stay cool even when physically engaged, and tell the person (or animal) to knock it off in a calm but take-no-bs voice. Panic or anger only escalate things further. Even when your adrenaline is up, you have to do your best not to show it. But if you can sound calm, the other person may stop struggling sooner.
Note 1: my voice stays nice and steady. My right eye may tic a bit if I'm really angry or scared, but my voice stays steady. This does take some practice....
With dogs or people, grabs work better from rear or flank. Easier to get the hold, harder for them to respond, and of course harder for them to see the tic in the right eye.
Note 2: hopefully, witness statements are in your favor when LEO's show up. I was very happy that they were, in the one case where things got to that point.
Note 3: Aikido, judo and ju-jitsu are really useful arts for learning how to stop somebody without necessarily having to do lasting physical damage. Option to do damage exists, but a lot of that depends on the other guy.
Here's a question for the CCW holders here: If you are really worried about defense of self and others, how much time do you spend on physical fitness and martial arts training? Situations which justify use of limited force are much more common that those which justify deadly force. And I'd hate to think that people in the forum would choose to draw a weapon because it's their only viable option for a physical intervention.