Don't give up. Try every day. People DO cancel, you never know! On our last trip we had a reservation for 14 people. A little girl in our party dropped a bottle of apple juice on her foot and needed stitches. So we had to lower the party size down to 11 - which opened up a table for a party of 3 at the last minute!
Disney was very nice to that little girl - when I explained what had happened they packed up a wishing star, a wand, a sword, a coloring menu and some crayons to bring back to her. She recovered very quickly and was able to enjoy the rest of the trip!