Consider whether John could move to Canada. That might be cheaper and just about infinitely simpler. You are potentially looking at tens of thousands of dollars in legal fees to get this sorted out by a highly specialized lawyer firmlaw-firm, and there is no guarantee of success, especially if you just leave in a hurry. If you stay put and have the lawyer sort things out first, it's a lot better but still expensive and it won't be fast (think of many months, possibly years). Not to mention if there are unpaid taxes then the most you can expect from a very good lawyer is avoiding jail time and decreasing the immense penalties a bit but certainly there will be some very interesting amount of monies to pay to IRS (and potentially state/local too).
Edit: I would talk to a lawyer first, no matter which direction you want to go. Initial consultation should not be horridhorribly expensive.