This happened to me once. AMEX and I worked things out. They overnighted a card to me and gave me a number to call if I really had to make a purchase. They were

This happened to me once. AMEX and I worked things out. They overnighted a card to me and gave me a number to call if I really had to make a purchase. They were going to generate a one time use card number and the merchant could punch it in. I never did need it though. I just waited for the replacement to arrive the following morning.