That is a good worry for the sellers to have. I have had Banks go after Clients after the closing and it may happen when you think it is all done.The banks need to write a letter letting seller out of loan and saying they will not come after them. The Seller can cancel the contract at any time if the Lender will not write the letter. What if you tell them the Bank will not come after them and 6 months later they garnish the Sellers wages with out warning? I know of this happening.
Short Sales are risky and who knows the Lender may not approve the short sale anyways. I think they should sign it and see what the lender says. If the lender will not write the letter saying they will not come back on sellers, then cancel agreement. Read Short Sale Add.