H1b Transfer rejection after joining new company


I am already in US working for company called XYZ for last 1.5 years. I have transferred by H1B to new company called ABC[Big MNC].

My H1b transfer petition is done under regular processing. And my new employer is asking me to join after the receipt number before the approval of H1b transfer petition.

What is the process and steps , I have to follow if my H1b transfer petition is rejected after joining new employer. Do I have to go back to INDIA my home country if my H1b transfer petition gets rejecting after joining new company ?

What is the probability of getting rejection in H1b transfer petition. My new employer is big MNC. And I have bachelor of engineering degree in INDIA with clean other record.

Its impossible to predict probabilities. Its almost always recommended to wait for the approval before starting.