The other thing to keep in mind is that there is no reason why the copyright holder (i.e. casino would want your chips back. Certainly at least if we are talking about non - obsolete chips there is another gaming regulation that one has to consider. That is the regulation that they pay you the face value when you turn in the chip.

In the case of chips which the casinos have made obsolete, arguably that process could release any claim of ownership that the casino might have. But even if it didn't, why would they want the chip. It has no value to them if they can't sell it and who would buy it knowing that the casino could just take it back whenevre they wanted.

Therefore I have no concern that anyone from a casino is going to come knocking at my door.

And as for the estoppel issue, I think that goes double for any casino which has ever issued a chip commemorating a Casino Chip Collecting Convention.