Thier responsibilities? Not sure I'm following. I believe it possible to work out an agreement for repayment of a state's portion of the debt, etc, but what continued responsibilities do they have? They are not mere members of a league. They are parties to a compact.
As are we in NATO and certain trade alliances, no doubt. It does not abrogate our right to withdraw if such institutions become abusive in our eyes. An important distinction to make, since a governing body would never admit to such abusiveness.
I'm not talking about money. They ratified and assented to a Constitution to which they are bound.
You are way off.