As a Licensed Realtor in New York State (Buffalo / Amherst area actually), I would pretty much agree with Mack (as I usually do - pretty smart West Coast broker, he is!). Look at the contract - are there any contingencies that have not been met and have since expired (mortgage commitment, inspection clause). If you signed a contract and gave the buyer the right and the time to do something (get financing, home inspection) then you must allow that time to pass.
If this is in the beginning of the process, you can have your attorney cancel the deal.
I'm sure you are using an attorney, as we are an attorney state. Consult them and ask the question. They will know the answer based on your situation.