Ooh! From their FAQS
http://www.restaurant.com/help.asp?png=x#10
What do I do if I attempt to use a Gift Certificate and the restaurant is closed or not accepting my Gift Certificate?
This is a rare issue but sometimes restaurants go out of business or change owners without informing Restaurant.com. If you attempt to use a valid Restaurant.com Gift Certificate and the restaurant is closed or not accepting your certificate, please contact our customer service department. You may reach them by email at
info@restaurant.com (include your Gift Certificate number) or call 800.979.8985 (M-F 9 AM 5 PM CST).
Our customer service department will exchange your unused Gift Certificate for a credit to Restaurant.com. This will allow you to choose another restaurant or merchant certificate from Restaurant.com. We appreciate your assistance in keeping our site as up-to-date as possible. You can help other Restaurant.com customers by informing us about your experience.