We will never know because we are not casino owner so the best answer should come from casino owners whether they are making money or losing money when bitcoin's price drops.
Perhaps we can speculate but I do not know how to speculate about it since I have no idea how casinos manage their bankroll.
There is also no researches about how bitcoin price movement affect gamblers, in this specific case where the price drops, we do not know how gamblers deal with it.
Whether they keep on gambling or they stop for a while when the price drops, but I think it does not really affect gamblers because there are alternative coins to play if they do not want to play with their bitcoins.