I don't think I would lay my gun down unless the police were already watching me. I think I would try to put it back into its concealed position, and I would try to do that when no one was watching me. Maybe best to not actually draw unless in immediate danger. Hearing shots at the far end of a huge store does not mean I am in immediate danger.
That's easy to say. Have you been in an area when a shooting is going on? I have.
It's total chaos. The first shot or two on't register. You'll be processing what is happening. Then you'll try to a safe location. The next thing you'll do is try and secure your location once you are safer. If you're armed, I promise you you'll reach for your gun. If not, you'll be swearing that you weren't armed (and it's why I avoid so called "gun free zones" as I was in one during the shooting) and why "gun free zones" should be illegal. After that, what you do depends on how your body reacts. Some will freak out, while some of us will have the fight instinct kick in.
Shooters can cover a lot of ground before the police arrived. They can reload, and cause a lot of terror in a short time. They can reload because they have the advantage over the public, and since they aren't thinking rationally they're like sharks going after chum.
Having been there, my advice is to get cover, help those around you, get someone to call 911 while you cover your area, then when police arrive make it clear you're a good guy. Communication is your friend. It'll feel like slow motion and when you're done you'll be shaking for days or longer.
I can tell you that my incident was at the college I taught at and it was rough going back to that campus. In fact, it's been hard to go to malls, and other places with large crowds. And in some ways after the incident will be harder than the actual shooting. So you can guess what you'd do, but I'd suggest you learn more, that you realize that it's easy to say things, and that things never go as planned. If they did, I'd have been armed and the shooter would be in the ground and not prison, but I didn't have a crystal ball and I'm now willing to risk my freedom so I followed the law and almost died because of it. But the rest of the story is off topic for this discussion.
So I'll just say, please cut the BS, and try to learn all you can because in a shooting you only have seconds to react and minutes until the police arrive. What you do between the two determines if you and those around you live or die.