If you sponsor an employee as a US employer, the right of such employee to live and work in the United States is tied to the application you filed on his behalf and that is currently being processed by the Bureau of Citizenship and Immigration Services.

In a situation like the one you present in your question, it is your obligation as petitioner to notify the Bureau of Immigration and Citizenship Services that the employee you filed a petition for alien worker is no longer your employee and therefore you are withdrawing the petition.

Because an alien worker has rights under the Labor Laws and for this particular type of visas the employer is responsible for paying some costs associated with the Alien’s need to return to his/her country as all other labor law benefits extensive to workers who are laid off or in the event that they have willfully disengage for personal or professional reasons.

Until you notify the Service of the fact that the employee is no longer working for you, you are still the sponsor and you are responsible before the Immigration authorities to fulfill all the obligations you contracted at the time you filed the application with the Government and with the alien worker.