Hi Andrew,
I have applied my Green Card from 'A' Company in 2007 under concurrent filing and the i-140 got approved in Jan'2010.I had query in feb'2010 for I-485 about the employment and it is been answered in time and the application has been pending(PD is 2004 Jan).I have got a new employment offer from 'B' and they are planning to apply AC-21.

Is there any chance that Employer can revoke i-140? What happens if he does?
Right now I dont have H1 Visa from company 'A' and I am using EAD only.The New Company 'B' is also planning to apply new H1-B , back up for EAD. Can i hold EAD and H1B same time?
How about having EAD and H1B status and payroll?
(I dont want to use H1B visa , just for a back up). is it valid?

Thank you very much in advance.