IIRC under current tax code this results in $100k of taxable income for the original debtor. For C, well, getting paid from the charity counts as taxable income, so things net out. Donate $100k, receive $100k in debt repayments, net change to AGI is $0.
The best scheme I can come up with is this:
Make the note performing again by giving the creditor a small amount of money. Claim that it is now worth significantly more than $10k due to being a performing loan. Donate the loan to a controlled charity, pocket the tax deduction for the "fair market value" of it, and then stop paying to make it be "performing" and have the charity take the losses on it. The IRS will still fault it, probably, but it lets you actually get ahead on your taxes.
NB: this system can be a price support for rare artwork getting sold in distress. If you think you can claim to the IRS that a piece of art is worth $100M later, and you pay a 30% marginal tax rate, then the post-donation after-tax price is essentially $30M less.