The *only* circumstances under which you could be sued, if there was no relocation contract or repayment clause, would be if you received relocation assistance and/or a relocation bonus from the company and there was some evidence or reason to think that you never intended to keep the job but only took it so as to get the assistance or the bonus. In that case, if you never intended to keep the job but led the employer to believe that you would, you could potentially be considered to have committed fraud.