If it's declared legal tender, with a value declared by Congress? Oh, anyone with an outstanding debt that needed to be paid.
You have two choices: Accept the legal tender when offered, or accept nothing, and consider your debt paid in full, with no recourse after that.
There needs to be a Constitutional Amendment that states that Congress isn't allowed to "declare" (regulate) the value of anything at all.
That is called bankruptcy .They may think they can do what ever they want with ink and paper but that kind of shit would not pass anywhere.If the USA government does such a thing 3 minutes later the banks will be full of people wanting to change their "american paper" with some other currency.And that means say hello to inflation.