"Kostas on the Beach" is open from the 25th Oct. - Arillas Beach point will be open for some afternoons but , maybe , only weekend evenings for food. Armourada will serve you a beer or two , in the afternoon, but not sure if food is available in the evening. Suggest that you look into Marvel Hotel, next to Rainbow , and speak with Costa there. Sometimes , if you give him enough notice , he can get a good evening meal sorted for you.
If you have transport then Mon Amour, Kavadaddes , will look after you as will "Bavias" and a few other places in Sidari.
Not sure if Graziella will still be open on the 20th but you should also check Brouklis or Thalassa.
Cheers
Negg