-You need to talk to your current employer and the lawyer about your leaving and ask them not to withdraw the I-140. Try to make them understand your choice.
If they feel not good and will withdraw I-140, you have to ask the new employer to file a new I-140 for you. You must make sure the new employer will file a new EB-1b I-140 for you before you move on. Otherwise, I suggest you to stay with yopur current employer until your I-140 is approved.
If I were you, I would wait for the I-140 approval and then consider changing job later.