Money back
The woman who purchased the painting in the auction the moment before it was shredded got her money back in the end. In her eyes, she didn’t want anything to do with a painting that was half destroyed, it was worthless to her. But the auction kept it and didn’t want to throw it out just yet.
After all, someone there was clever enough to see that this was a media stunt by Banksy to gather more attention. That means that this painting was now even more famous than ever before and perhaps it didn’t really matter if it was partially cut up. There may still be some value there.