Tell me the law you believe would have prevented Paddock from killing a lot of people. Unless you can explain that, there isn't a reason for another gun law.
The question isn't what kind of law could have stopped Paddock. I doubt any law could have stopped Paddock; his MO was unique and everyone knows that every dog has one free bite. The law isn't looking for folks without criminal records, who do not bear elements of suspicion. The police only find who they're looking for.
No, the question is what sorts of laws and protections can stop the copycats. We now have the ghastly model of a methodical killer sniping at strangers from the high floors of a building. That's an open invitation to copycats. We will be seeing hotels requiring folks to go through metal detectors, hotels requiring guests to keep guns in gun safes and not in guest rooms, and hotels and other public spaces banning the carrying of firearms.
As for the implement of destruction, why shouldn't it be subject to regulation? I don't advocate restrictions on the frequency of gun purchases or the size of a gun collection, but I sure as hell advocate registration and insurance. The same basic regime we require of those we permit to drive cars on public streets. Guns, like cars, are useful but dangerous implements and should be registered with the authorities and made subject to a requirement that their owners insure them with respect to the potential mayhem they can cause.