If an immigration lawyer has already reviewed the facts and advised him, that's as strong an opinion as he's going to be able to get.
With this being a single offense, pled down to disorderly conduct, I would anticipate that he won't have problems returning to the U.S., but I think that he should have with him court documents confirming the disposition of his case "just in case". Also, we can only speak about his chances or odds -- and sometimes the unexpected happens. If he's still nervous, his best bet is to have a follow-up consultation with the lawyer who has already reviewed the facts and advised him in relation to this case.

