Ginnu,
That was a very good document. I guess, it clearly states how USCIS should handle the cases. Points to note:
"It is expected that the alien will have submitted evidence to
the office having jurisdiction over the pending Form I-485 that the new offer of employment is
in the same or similar occupational classification as the offer of employment for which the
petition was filed. Accordingly, if the underlying approved Form I-140 is withdrawn, and the
alien has not submitted evidence of a new qualifying offer of employment, the adjudicating
officer must issue a Notice of Intent to Deny the pending Form I-485."
So, it clearly states that if the employer withdraws the I-140 after 6 months, then the applicant has to inform the USCIS about the job change and if not, the USCIS will issue and "Intent to Deny". But if the previous employer doesn't care abt the I-140 and it remains valid, then the BCIS appreciates the candidate filing AC21 about the job.
Thanks,
Piske