correction
>1. laid off or resign after 180 days I485 pending
I-485 remained unadjudicated for 180 days or more. You can leave your original petitioner anytime. The problem is, if you leave and the BCIS will adjudicate your petition before 180 days into I-485 ( read: "a miracle will happen" ), then your I-485 will receive a "Notice of Intent to Deny".
>3. inform INS before INS processes 485 the case.
Only if the underlying approved Form I-140 is withdrawn before the date that the Form I-485 has been pending 180 days.
HTH.
P.S.: "I am not a lawyer, etc..."