IMHO bankruptcy should be used as an absolute last resort only. Filing bankruptcy will ruin your credit for at least 7 - 10 years. Credit is EXTREMELY important, take it from one who used to not use credit wisely
but is now well on her way to have A+ credit
Has he attempted to work out a payment arrangement with the court? Sometimes they will allow you to pay an additional percentage of your current child support payment to go towards arrears. Plus tax returns can be seized to help pay it off. I have a friend who paid off his entire arrearages with his tax returns. These large payments help bring the interest down considerably.
I'm sure his fears about being jailed are very genuine and real. I think you're correct also, it's pretty hard to pay a debt when you're behind bars. But that's the law currently. The best thing to do is make some sort of effort to pay on it. Just letting it go will only increase his problems further.