house sale contract

Buyer and seller entered a house sale contract pending on approval of short sale when the loan is held in bank A.
Bank A transferred the loan to Bank B right after Bank A's approval, whick took several months. Bank B will do the approval process again.

Now the seller wants to do the deed in lieu to get rid of the loan quickly. Then the buyer won't be able to buy the house with the contract. Can the buyer sue the seller?

The key here is the contract is pending on approval of short sale. Seller may argue he made reasonable effort to get approval, but seller is obligated to make every effort to get approval.