Urgent H1B transfer issue!!!

Hey,
My case is very complicated. I really appreciate your professional input.

I worked for Univ. A with H1B and moved to Univ. B recently. H1B transfer is in progress. However, the current job is not satisfactory, so I decide to move back to Univ. A.

what I know is that H1B transfer from A to B is in progress. Univ. A has not reported anything to USCIS yet and entered my visa status as "visa leave".

My question is whether I can go back to Univ. A immediately after I terminate my employment at Univ. B without H1B retransfer back.
If this is impossible, how can I work at Univ. A quickly and legally?

Thank you a lot!