Any item has a 'value'. If the casino did not allow its use, or cash it in for value, regardless of the status, then the chip as a possession is forfeited. I did not suggest that they couldn't cancel the promotion, I only suggested that once the chip was properly cancelled (however that may be) the the representative token of value (in this case the chip) may not be confiscated without proper consideration.

Property law says all land is ultimately the property of the State. Your house sits on land that the State has a higher possessory claim. US law requires the State to fairly compensate a person for any property it reclaims.

The claim of the casino over the chip is certainly no greater. The casino may not have had to honor it, but they certainly had no right to confiscate it without due consideration.

You write me a check, I don't cash it for 6 years, you (or your bank) may properly refuse to honor the check, but I keep the instrument nonetheless.