Actually dining credits are a little different, they specify a meal in a specific specialty dining room. If the price changes you still get a free meal. A refund of a HIA meal never goes to non-refundable OBC.
I actually don't expect to get any of it back in OBC that can be used for other items. I'm not sure if there was another tag attached to those specific funds so they could be used for anything else.. I didn't try to test the system, I just purchased another excursion. It would be interesting to know the official answer.