As per the regulations dated 17, January 2017 the moment your I-140 is approved the priority date is your property not the employers. Therefore even if the I-140 is revoked the same day and if it was approved, that priority date is yours to keep. You can take it across to any employer. If you go to another employer and if yours is a labor cert based case being filed you have to redo the PERM and the I-140 but you will carry the old priority date which is a big advantage.
In addition to your priority date, if the I-140 remains approved for 180 days, you can continue to extend your H-1B with any employer after six years. They cannot take that right away even if they revoke your I-140.