Well....I think your damages will depend on intent. If he was behind and intended to bring the loan current (perhaps by renting it out) then I would say that's fair. If he executed a 12-month lease knowing that he would be walking away and just pocketing the rent.....that's a felony. Problem is your damages are against someone who might not have any money to pay you.
I would suggest that you contact a real estate attorney if this has caused you extra expenses and see what the attorney thinks.
I'm sorry....it's really tough out there! I hope it all works out for you.