We have had several occasions with only 3 showing up on a reservation for 4 at the credit-card-hold character buffet restaurants like Crystal Palace. We were not charged the $10 for the 4th person not showing up.
However, last time we ate at Cinderella's Castle, the group in front of us at check in were asking for a refund for 2 in their group that had not made it due to airplane connections (storms cancelled 100s of flights) The check-in person had them step aside to wait for a manager so they did not immediately get a no-refund message. Disney must at least consider whether or not to give credits. Don't know how that particular case resolved, because we were called back for pictures before the manager showed up, but sounds like there is at least a chance they will refund on the pre-paid if it's a real reason for cancelling (the cancelled flights story was certainly plausible since it was all over the national news at the time.)