Havent been following this thread so sorry if this was already reported. I originally got credit in southwest by booking a flight, cancelling, and keeping funds for later (before gc was confirmed to work). After cancelling the card I used the funds on a $200 flight segment. A few weeks later the fare decreased to $170 - I switched to the new fare and i was given two options - keep funds for later or credit my original cc. I figured I wouldnt have use for the $30 so it was worth a shot to credit it to my cancelled cc. A few days later I had a credit on the gold card and after emailing them I was issued a $30 refund check.
Long story short - while it's been reported that there is clawback for the airline credit, I believe that they do not claw back the credit after the cc was closed. Could be that they would be more diligent with this if the credit was $200...