From AA's Contract of Carriage:

"When your flight is canceled or a delay could cause you to miss your connection, we'll rebook you on the next American Airlines flight with available seats at no additional cost. If no American flights are available until the next day, and the disruption is caused by us, we’ll rebook you on one of our partner airlines with available seats at no additional cost. We’ll rebook you in your originally ticketed cabin or class with your original form of payment.


"If your flight was delayed or canceled and you don’t accept our alternative arrangements, or none were available, we'll refund the remaining ticket value and any optional fees according to our involuntary refunds policy. Beyond that, we have no further contractual obligation."

(Emphasis added.)