Restaurant.com certificates don't expire anymore no matter what state you're in.
If you have old certificates that you've never used and are expired according to what's printed on the certificate, you should be able to go into your account and print new certificates without an expiration date on them. If you have a certificate with no expiration printed on it at all, then theoretically you should be able to use it forever.
The only exception is for restaurants that no longer participate in the program and refuse to accept its certificates. If this happens, Restaurant.com will give you credit towards a new certificate at a different restaurant.