F1 to H1 transition ( H1b approved and job ended)

[shr215]

I am in F-1 STEM OPT, my H1B got approved under 2019 CAP for Company A. However, my job was terminated on July 15th with Company A. But Company A is giving me an option to revoke my approved H1 either before October 1st or after October 1st. 

My STEM OPT is valid until February 2021. 

1) What if my H1B is revoked before October 1st? 
a) What are the steps I need to take to keep my OPT valid? 
b) If it is revoked before October, then would my OPT continue by default? 

2) What if my H1B is revoked after October 1st? 
a) Will my OPT be still valid? (As H1 is approved and is not withdrawn and not employed with Company A anymore) 
b) I have started working with Company B on my OPT from September, can Company B apply for the transfer of approved H1B petition after October 1st? 

Would you recommend revoking my H1 before or October 1st? 

What are my options to stay in status either in OPT or H1? 

What are my options to become CAP exempt? As I am left with only one chance for filing H1, I am looking to keep my H1 to be exempt from CAP if possible. 

Any input is really appreciated. 

Thanks