I stopped filing my taxes starting in 2011 for 2010. I had always hated the process, but in 2010 I had switched jobs several times, and had misplaced one of the stubs mailed by an employer. I have almost always worked as an employee, not a contractor or business, so I did not owe money--they probably owed me. I decided that rather than get the couple hundred bucks I would receive as my return, I will forgo the stupid…
You may want to consult a tax attorney, if you haven't already...
He won't get in trouble or anything.
They will calculate a substitute return and mail it to him. If it shows a refund he can chose to accept, reject, or ignore it.
Accept: They'll send him money. But not as much as if he had done the return himself.
Reject: You do that by filing a correct return.
Ignore: Then he's giving a free gift to the government. Which is his choice I guess.
PS. He may regret his decision later if he wants to get a loan, or apply for government services.