Casinos have plenty enough slot machines to average out any swings in profit/loss. I doubt the variance is that large overall.

Some time ago, I remember reading a talk given by a Las Vegas casino operator during a conference on risk. They analyzed their top ten largest losses for the previous year, and found none of them were associated with their gambling results. The events that actually cost them were completely unrelated occurrences, like their resident entertainer getting savaged by a tiger, large fines from the gambling commission because of an incompetent employee, and so on. The gambling side of the business generated remarkably smooth results.