I don't know what you mean by 'go backward'. Do you mean after you have uncovered a square? No, once the mine goes off you're done.
No sorry, I mean trade points on the game back to BTC.
No, I don't think so. That would be a violation of Facebook TOS as I understand it.
This is simply another place to spend your BTC, and a pretty effective implementation he's done too. If only we could get all app developers to do it.