You should have worked it into the contract with the hotel that by x date, if the rooms that you "reserved" are released back to their general population SO THAT you don't have to pay for them. I always make sure. The two conventions I organized as well as my wedding... 2-3 weeks before the event, the hotel gets those rooms back and I don't have to pay if they go unused. Worth calling the hotel NOW to see if they'll let you do that. If anyone wants a room after you call, they're on their own... enough is enough