Dude if you don't like your current situation go for it. I can't stand my situation so as soon as I get the EAD card I'm out of my "sponsoring" Company. If you are happy don't switch!
The employer does have some control. If they request the revocation at any time before GC approval and you don't prove that you have a "same or similar" job or job offer, the I-140 will be denied.I think the employer does not have control over to revoke I-140 beyond 180 days of filing 485.
Is this true?