Current H1 expiring soon, H1 transfer

[happygolucky]

My current H1b with company A expires in Oct. I have an offer from company B and would like to move ahead with that.
Company B will file for my H1 transfer. Company A will also be filing for my H1 extension. Both will be regular processing
due to hold on premium processing. Now my question is this:

Let's say I join company B after transfer receipt notice is received. If the H1 transfer is not approved by Oct, will I be out of status?