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concur with your response. But wish to modify your response a little. Actually he can legally work after O-1 expires in Feb. For most employment based AOS, the immigration law permits status violation such as unauthorized employment for up to 180 days since his last lawful admission.

-If his O-1 expires and has no EAD, his work is illegal (unlawful) though it does not affect his I-485 approval if the unlawful employment is less than 180 days. So, the employer probably will not employ him to work if his O-1 expires and he has no EAD. Otherwise, if DOL find it, the employer will be fined or punished.

 I am certain he will get his EAD before the cut off. So just stop working in the unlikely event that the EAD is pending after 180 days. 
USCIS does not issue emergency AP readily. He has to meet one of the guidelines for the issuance of emergency AP.  Again I don't think he needs it because the AP will be issued way before May.