Yes, one of the main dining rooms should be open. You'll have to go to them to see which one as they don't advertise it. We had a wonderful, quiet, peaceful lunch on embarkation day for our TA in April. There were only about 10 poeple in the whole dining room. It will only be open during the regular lunch hours which I think end at 1pm.
They do have one DR open & will accommodate all the b2b cruisers and as many people as they can handle comfortably with the staff they have. At the time when it becomes to much to handle they shut the doors & direct other to the Horizon.