Travel with old H1/H4 stamping and new i797

My wife’s H1B expires in June 2021.
My H4 EAD expires on the same date.
We have to travel to India in Feb and March 2021.
We plan apply for H1B extension(premium processing) and get an approval before de leave for India. We also plan to get H1 and H4 stamping done in India(we are eligible for drop box application) in Feb 2021.
When we return to US during March 2021 before the current H1 expires what will be the i94 validity?
Will it be based on the latest H1(newly stamped) or current H1?
If i94 based on the current H1 (June 2021) can we travel outside before it expires and renter on the new H1/H4 visa?

It will be based on the new approval that you get from your employer for H1B extension.

Now, if you return before June 2021, you can technically use the old visa that is valid until June 2021 to re-enter. The only catch is, next time you travel out you need get new stamping.
Also, You get a new I-94 when you exit and re-enter the country.