As far as I know,no one mentioned that a company can not revoke I-140 after the I-140 is pending for 180 days.I took a lot of time to do the reaserch,till now I did not find any clue which says I-140 can not be revoked after pending for 180 days.
Maybe your attoney is right,but I hope you had better to do some research because this step is VERY important to you.Please let me know after you get final answer.