That is a tricky one, even ESPN and Big River close around 11pm. You say you are arriving at the BW but from your signature it looks like you're staying at the Dolphin?? Picabu Buffeteria at the Dolphin is open 24 hours, but only serves pre-packaged sandwiches, salads and desserts after dinner hours. I don't know of anywhere else in the Epcot resort area that serves food after midnight.
You might also want to consider grabbing something at the airport to take back with you.