Here is an excerpt from some forums:
"The INS has typically been taking several months to process H1B
revocation notices, which means that, as a practical matter, the revocation
of the H1B petition may not appear in the INS system for several months."

src; http://www.murthy.com/news/UDtermh1.html

So in worst case, even if your employer sent a revocation application to USCIS, there should not be a problem in transferring  h1B. I am quiet not sure about how long can we stay without payroll in h1B.  I have heard lot of stories like, we cant be in h1b withour payroll (not even a single day), also heard that there has been a successful h1b transfer without payroll for 2 months etc etc. I welcome other experts to speak in this case.....

good luck