In the movie Ocean's 13, they rig every game in the casino in order for Bank to lose as much as possible. But once everyone is on a winning streak, Danny gives the green light to start the "earthquake", forcing Bank to go to the room where the Greco is stored and forcing it to reboot due to the magnetron in his cell phone. But in the 3 minute window when the system is dowm, everyone wins big but no one ever cashes out! Only when the earthquake intensifies do we see all of them running to the exit with chips, not cash. Rusty does call out to everyone around him to cash in but there's a stampede of people getting out, and not waiting to cash in. Since most of them didn't cash-in, Bank could easily change the chips the next day, causing the existing chips to be worthless, just like the movie 21. So my question is; did Bank really lose 500 million that night?
I don't think people would have waited till next day to cash in the chips. There was big money at stake. Soon after the earth-quake had settled (which was only a few minutes), people would have went in to cash in the chips. Also, I don't think casinos can just change the chips without any reason. There definitely was fraud and Willy Bank knew it but the problem is he can not prove it. So he is bound to pay everyone with their win.