Employer change while H1B extension is in progress

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I am having approved i140 with Employer A and my i94 is already expired. Employer A filed and extension and awaiting USCIS’s decision. Got an offer with Employer B and they agreed to wait until my H1B transfer plus extension is successful and then proceed with resignation formalities with Employer A.
In this situation if the Transfer plus Extension petition that got filed with Employer B gets denied can I continue working in USA for Employer A or should I leave the country??