Make a new ADR before you cancel the existing one. If you cannot get a new ADR at the same place, keep the existing one (don't even mention it at this time). When you hang up the phone, consider the options -plan to go to the original ADR with the remaining members of your party and see what happens, or make a new ADR (using a different phone number) at another restaurant just in case you are turned away at your first choice when you get there. You will probably be seated at your first choice, CMs know that things happen and that some party members may not show up.