Why? I would challenge the feds to go ahead and see if it is anyplace I can access and thereby prove that it is NOT lost. Then, in ten years it might be accidentally *cough* found *cough* and more reasonably dispensed with without fed intervention that time around. Probably to someone with a residence not in this country that could afford the purchase price and where the feds could yap all they might but would not be able to get it back.
The cat is out of the bag. If the coin were to disappear at this point, the government would probably sue Mr. Lawrence for the appraised value under a theory of conversion. It was in his possession and now it isn’t. The fact that he can’t find it, does not mean he did not owe a duty to preserve it until the ownership issue is resolved.