lay off within 180 days
As I spoke to couple of attorneys, the impression is that if you get laid off before 180 days then you can join any company with the EAD, provided the new job description matches the one in the labor certification that was filed for Green Card. 180 days period applies, only when you voluntarily change your job. And as everybody says, it depends on the immigration officer. And if you get a RFE, there is a good chance of getting the GC after you change the company.