I don't know what you mean but to add additional context, the PERM process takes ~1 year and the employee is free to leave before / during / after the process. It is not exceptionally hard as an employee on a H1 to have an employer sponsor PERM for you, most (90+%?) employers do it, so it's not an added draw towards Facebook if they do sponsor the PERM / GC.
If they leave after the PERM + I-140 have been approved, companies have a limited period of time to revoke the I-140 but this is extremely rare and won't happen unless the employee has really burned their bridges. Six months (afaik) after the I-140 has been approved, the company can no longer do anything about it, the employee can leave without any immigration related ramifications.
If they leave after the PERM + I-140 have been approved, companies have a limited period of time to revoke the I-140 but this is extremely rare and won't happen unless the employee has really burned their bridges. Six months (afaik) after the I-140 has been approved, the company can no longer do anything about it, the employee can leave without any immigration related ramifications.