ask him to return in the same status that he went out of US with. That will be accepted at port of entry.
GC arrived after he had left , so did he leave while in H1 status , was he maintaining his H1 just before he left ? If he was on EAD , he shouldn't have left without AP in the first place and that means the 485 app can be considered abandoned by USCIS, but in his case he already has the GC so what will they abandon now

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Also can he ask someone here to post his GC to him in India, which that he will have no issues whatsoever anyways (only if the card is issued and someone can send it to him)