Huge, probably insurmountable legal uphill battle:
1) Prove that, but for MBs response, plaintiff would not have been injured
2) Prove that MB has a legal duty beyond normal security measures to stop an incident like this
3) Prove MB response was outside industry norms
That is off the top of my head. LV hotel lawyers are like Disney lawyers. They are the sharks that the rest of the sharks are scared to death of.
This is a flyer of a suit in the hopes the hotel will settle to make them go away. In the next month or so you will see everyone for a 1 square mile area sued, including other festival-goers who have a few bucks, the performers, the managers, the roadies, the fence makers, the people who make the coolers that were used to keep beer cold, the vendors, , people gambling downstairs, all the people who were on that floor, everyone.
It is the American way.
Now certainly made more complicated by the apparent fact that the "security guard" may not have been on MB's payroll nor on its communications network.
The plaintiffs won’t have to prove the things you list. All they will have to prove is that MB didn’t call the cops as soon as they knew there was a shooting at their property.
The emotions of the jury will do the rest.
You can take that to the bank.