Christmas dinner in Atlanta
Most of the hotels in town are likely to have something - St. Regis, Ritz Carlton Buckhead, Intercontinental, etc . . . but there are restaurants that should be open also.
Don't know how far into town you are willing to drive but Murphy's in Virginia-Highlands has a wonderful Christmas dinner. Also, Ruths Chris in Sandy Springs tends to be open on holidays and serves both its regular menu and a holiday menu with more traditional fare.
Sandy Springs Cafe
6065 Roswell Rd NE Ste 100, Atlanta, GA 30328