How many days I can stay in US after H1 amendment rejected

My Employer filed my H1 amendment and it is now on “Request for Additional Evidence Was Mailed”. In this situation, I would like know how many days I can stay in US if my amendment rejected even after my employer submit the details. And what are the possible option left to me ? My original petition and VISA is valid till Sept 2018. So

a) Can I stay back in US at least for 60 days grace period ?

b) Is it possible to transfer H1 after rejection of amendment ? If yes, In how many days ?

c) Or can my employer file the petition again ? If yes, In how many days ?

Thanks