"He was told as long as the casino is open they will trade chips at the tables."
Im sure he was probably told "As long as the casino is open AND THE CHIPS ARE CURRENT they will trade chips at the tables."
Most casinos would probably gamble on $5 chips being cashable, if you were only offering 20, particularly if they thought you were going to play.
I think it would have been a different story if he had put down a stack of quarters and $100's