Information on Grace period for H1B.

Hello, I worked for employer A till mid Feb 2018. My petition with employer A was approved till jun 2020. I joined employer B in feb 2018 on receipt. My H1B transfer is yet not approved for employer B. Now I have a better offer from employer C and want to join them. But I cannot join employer C till the time my H1B transfer for employer B is not approved. what all options do I have? I am worried that I might get rejection on premium processing. Will I have any grace period if my premium processing gets rejected? Recently I came to know that my previous approved petition with employer A has been revoked with the message “We revoked our approval of your case”. Does 60 days grace period still apply in my case?