Regarding the current VISA extension status - If the travel before i receive my extension

[SI17]

Hi All, 

I am on a H1B VISA  and 10-DEC-2017 is my current VISA max-out. I have a approved i-140 (15-OCT-2015 as priority date).

My current  project is get  over by 20-DEC-2017 and i have be asked to travel if there is no future assignment.

My  H1-B extension has been applied on 25-SEP-2017 and current its in "Application received status"  - normal processing.

With this above scenario - 

If I travel on 20-DEC-2017 (i.e. - with the current VISA expired on 10-DEC-2017) will the  in-progress H1-B extension go through or will USCIS cancel my extension with the reason "Applicant not in USA".

Please share your thought/ experience.

Thanks,

J