请教: H1b extend after 6 years

I already used up almost 5 years H1b time. Perm was approved and 140 is pending.

I really want to find a new job and change, but I only have one year H1b left. My question is: if I switch after my current 140 is approved, then could I use this 140 approval notice and ask for another 3 year H1b extension?

If I don't do that, I am afraid one year H1b time won't be enough for another set of PERM/140, even a new company want to do that for me.

And, is it usual for companies to revoke 140 after it get approved? What are the benefit for them to do it?

I suddenly found I am in a awkward situation.


Thank you for any advices!