H1B Amendment + Extension during Extension in progress

[KCReddie]

Any help is really appreciated.

[KCReddie]

Case Details:
i797 Expiry Date - 3/27/19
i94 Expiry Date - 4/6/19
H1 Extension Applied with Client A- 3/16/19
H1 Receipt Notice - 3/19/19
Got an offer with Client B - 04/10/19
Client B Start Date - 4/29/19
Upgraded to Premium Processing - 04/15/19
Note: Employer is same in all the cases

1. Considering we get an approval with Client A, we will go ahead and apply for the Amendment with Client B. This is a happy path. That being said, when are we going to apply for the Amendment - Before (or) After the H1 Extension approval with Client A?

2. If we get a RFE for the H1B Extension (Client A),

Can we still move to Client B and apply for the Amendment+Extension and withdraw/revoke the existing H1B extension petition with Client A.Is this a possible scenario? If yes, does the period of intended employment on the LCA stays the same i.e from 3/27/19 to 3/26/22. When do we need to apply for LCA and Amendment+Extension? Can we do concurrent Amendment+Extension filing before we get the decision on the existing H1B extension with Client A?

Does withdrawing old petition pose any immigration issues?What other options do I have to pursue the Client B offer?

3. If we get a denial for the H1B Extension (Client A), do I need to leave the country immediately as my i94 is expired?If yes, what are the options to come back to US? If no, what should I do without jeopardizing my current situation.

Thanks in advance for your time and inputs.