Here is my take: what if Kubrick wanted to dangle the illusion of an overarching order–something tangible at the end of the rainbow–but take it away? Davis, in an interview, said she somehow hurt herself in the circle, which is why the other gal took over in those scenes. But why not suppose the change was demanded by Kubrick himself?
There was no murder. I am increasingly convinced of it. Both times the girl warned him, men in masks were easily close enough to overhear her. Add this to the fact that even though Davis was apparently present in the orgy somewhere, that she was not the girl warning him, and what you have to conclude is that it WAS a charade, and that even though it was NOT the same girl who warned him who died, that Ziegler saw no reason to dissuade Dr. Bill from that possibility, since they wanted all the leverage they could get for him to keep his mouth shut. And it worked, more or less, since the fear and confusion caused him to break down when he saw the mask, and even if Nicole Kidman has been the one who secretly found it and left it out to see how he would react, she did not say. She loved him, I think I might say, convulsively, not patiently; reluctantly and perhaps by force of will.
And Kubrick, in the end, was saying there is no order at all. Good people like Domino get diseases, everyone else is running around chasing sex and things, and there is not even a despotic order ruling the whole thing: just a bunch of prurient and odd rich people with strange tastes they indulge from time to time, out of ennui and perhaps long-standing habit.
It is an odd joke, one he perhaps felt well content to make his last.