Sounds to me like the first path of attack would be to request a refund from restaurant.com....and if they deny your request, simply dispute the charge with your credit card company. It would seem easy enough that if what you received no longer has value, it should not have been available for purchase.

(Caveat - You noted that this certificate was for a local restaurant, which is probably the only type of restaurant for this would work. If the establishment has more than one location, even if one is in Florida and the other in Alaska, I wouldn't expect restaurant.com to refund your purchase given that there is indeed a location at which the certificate can be used.)