What is a "note" worth after the balloon payment was defaulted on?

Not sure if this is the right forum to ask the question in.

I have been carrying paper. The buyer is a millionaire broker and owner of real estate companies. He failed to make the balloon payment years ago but promised to pay up eventually.

Now he wants to walk away, leaving about $ 58,000 in unpaid interest following his default.

There is an offer to pay as if it was the due date for the balloon payment, ripping me off for $ 58,000.

Q: such a note is ultimately worthless, isn’t it? It boils down to a counter party’s integrity? - In that case, people need to hear about this and avoid such deals like the plague!

Was this note secured by a deed of trust or mortgage, and, if so why did you not foreclose?