please read AC21 carefully   180 days of 485 plus approved I140 is more safe enough to change job   Even if employer withdraws I140 it has no impact on 485 at all coz 180 days of 485 has already passed and AC21 protects it   The I140 180 days of approved date is only applicable when you have not filed for 485 application concurrently and you want yo change job then it’s highly required   I have repeated explained this multiple times in this DB