Well the employer can revoke the I-140 and then your friend won't be able to file for I-485 and he will need to find a new employer and get a new LC, then new I-140 and then I-485.
Ask your friend to lay low right now, be nice to the employer, have your friend offer to the employer that he files the 485 on his own, if he is able to pull that out, then after 180 days of filling the 485, tell your friend to tell him employer to F*C* OFF and find a new job and use AC21 and continue his I-485 with some nicer employer.