Short Sale Approved - Seller Won't Sell (Next Steps?)

[Jonathan Makovsky]

We have an approved short sale and the listing agent just informed us that he will not sell it anymore. Our contract is valid, enforceable and past any contingency periods. Our attorney advised us to file a lawsuit and a Lis Pendens on the property, which we will be doing. 

Has this happened to anyone else here? Any other advice/thoughts?

• Side notes:
• Our contract includes a provision for bank approval contingency.
• He owes about three-times what the property is worth and I don't believe he has made a mortgage payment in approximately three years.