I doubt he's going to jail for not paying a fine, but I am guessing he'll be served and forced to pay the fine plus fees via federal court order if he still refuses. The feds will win or find a way to win

Still refuse? That fine will show up on his credit report as a debt to the federal government after judgement. Try cleaning/clearing that on your credit report or try to get a loan - in a timely manner! I've seen 800-plus credit scores not get a loan for much less due to a tax/ lien or debt to the government. Not to mention how many eyes will be on him...

Take the lump(s), pay the fine and move on...