H1B Transfer close to I-94 expiry

[Aryan_H1B]

Hi,

I work for Company A who placed me in Company C (Client) through Company B. My current I-797 with Company A expires on 28-Nov-2018 and have I-140 approved with Company A.

Now Company C would like to hire me as a full time employee and started H1B transfer process on 31-Aug-2018 in premium processing and got RFE last week. And joining date for Company C is 21-Sep-2018 (this Fri).

Questions:
1. If I join Company C on 21-Sep and suppose H1B transfer denied after I join, what is the situation? Do I need to go back to India or can ask Company A to extend the H1B?
2. Can we have multiple H1B VISA processing at the sometime? that is H1B-Transfer and H1B-Extension in parallel? And can I choose which one to go for if both are approved?

And is it the safest approach to extend the Company C's joining date till I get decision on Company C's H1B transfer?