[dentist90]

Kinda like Mc Lovin said, in the sale of a business there are two ways to go. A share sale, which is a continuation of a limited corporation; or an asset sale, which is just buying the tables, chairs and goodwill.
If the restaraunt was sold as an incorporated company the liabilities are assumed by the new owners, and this includes staff liabilities, pending lawsuits and credits (gift cards) issued.
If the restaraunt was sold as an asset sale the sale price would be reduced by any outstanding liabilities.
The way I see it, the new owners cannot (and should not) be allowed to dishonour any gift certificates issued prior to the sale of the business. This should have been calculated into the sale price as an outstanding liability. I believe the new owners have erred in their interpretation of their liability either way.
Maybe speak to the new owner before the dine 'n dash?