Changing job on extended H1 based on approved I-140...

[SBabu]

I got my H1 extended for 3 years, beyond 6 years based on approved I-140. This extended H1 is valid till Dec 2018.
Can I join a new Employer with this H1? What if my current employer revoke the approved I-140?
Will this already extended H1 be valid till Dec 2018? My new Employer will start GC from beginning.