No, they won't do anything. There is something you can do, though. If you realize you're not going to be able to make it you could call Disney Dining (or if you have internet connection you could get online) and cancel your ADR, freeing up your spot for other diners.
No worries, though. I intentionally only booked one meal that has a credit card hold for our next visit because I just don't want the pressure/commitment. With nine people on our reservations, that would be a hefty charge, should we miss an ADR!