I truly wish I had more help.
That is awful that he is having to go through losing his other lines of credit as well. I have heard good and bad things from Amex on this board. Honestly, I don't ever care to have a relationship with them myself.
Maybe try searching for a higher up executive's email address and direct a letter to them explaning the situation. It could be useful. Sometime's you have to go over the front line CSR's heads to accomplish much.
With his relationship extending that long and his willingness to pay, I would still be inclined to think someone with more authority will be willing to help.