Change employer on approved H1B petition without joining the filing company

I have an approved petition for H1B from employer B. I am currently on L1B status with my current organization A and have a valid I94 till Dec 2019.

However, I am unable to join Employer B so far as there is some delay there due to re-organization with Employer B and have not accepted the position in E-verify.

Is it possible for me to use this approved petition from Employer B to go back to Employer A ? Or I only can join Employer B even if Employer A is willing to hire me back ? Is there a predefined timeframe which i have to stick to before changing employer ?