HOW DO I KEEP MY I-140?

         Question:

I have I-140 approved on Jan 2016 with employer A. I got another offer from employer B. Employer B is saying they will file my new GC after 12 months from my joining.
Can employer A revoke my I 140?
In case with my transfer I get H1B for year and need to file another extension where no new I 140 is filed, then can I get extension with old I 140?
Suppose by some magical change all dates become current as in 2008, can I still use old I140 which was filed by employer A?

Answer: 

Too many probabilities here for each answer.

Simple law. Yes, to the new employer. If the I 140 has been filed and approved for over 180 days, it can be used repeatedly many times for H1B extension. And the old employer can withdraw the I140 petition after you leave.