With Employer A(GC filing firm),Had valid H1, 140 approved on 5/2006, 485 filed 8/2007. 180+ days after filing 485,changed to employer B on AC 21 on EAD(also transferred H1 valid till 3/2011). Extended EAD now valid till 9/2010. Laid off by Employer B on 1/23/09, moving back to employer A on AC21, but Employer A had revoked my I-140 in 10/2008. Last pay stub of me is dated 1/23/2009 thru Employer B
1.What are the safe ways to be followed to move back to Employer A(GC sponsoring) without risking GC & status?

2. Does employer A need to file I-140 again to resume my GC process? If so is my priority dates change in case new 140 approved? What if new I-140 denied?

3. Can I transfer my current H1 from my emplyr B to A now when my last pay stub is dated 1/23/2009. (about 50 days old)