dschill. I am sorry about that whole situation. And that is a lot of money to write off. I really have no good advice. If he is an otherwise decent guy, just try to affirm him. He may simply be very embarrassed and feeling REALLY awful about what he owes you. If he feels that way, it is probably tough to even face someone you owe money to. If you can somehow contact him, and let him know you are not downright angry at him, and you understand how tough luck can happen. But tell him even a little at a time over the next while is suitable to you. It may save your friendship, and make him feel a lot more comfortable.
I ran a business in partnership with a guy a few years back. He was anal about sending bills, and circling the interest charges, and basically trying to shame them into paying. I bought him out, and I was much more understanding, and people appreciated this. I know what financial strain is, I have lived it. He had not, he was set up by daddy, so he never knew financial strain, and it showed in his expectations from the truly financially troubled farmers. Shaming is not going to work. Working with them, though there is no guarantee, MAY help. Heck, a couple guys owe me a bit after 5 years. Not a lot of money, but I know these guys are simply not having luck, so I just let it go. Compassion can be very important with some folks.
I hope there is some way to contact him. It is tough though, when they avoid you. He needs to feel comforted and affirmed that you are not spitting angry, and that he can talk to you, without embarrassment. and let him know you are glad to help him pay you up over time, so long as he TRIES!!!