I would consult a SC Broker or real estate attorney just to be sure but if the buyer agency agreement is expired and the agent failed to complete the blank in the agreement that states whether he is due a commission during a certain period of time after your agreement expires then you shouldn't have pay it. However, be especially careful if there is a clause in the buyer agency agreement that mentions that you didn't close because you defaulted in some way on your purchase agreement. I say this since you said you ended the purchase contract so you need to make sure you had a valid reason for ending the purchase contract. If you didn't have a valid reason for ending the purchase contract and it happened during the time the buyer agency agreement was in force then the agent may have a case for compensation. I would say it would be unlikely but you never know.
Allen Adams Realty