ll you need is to cut country off from the international financing,
At best, the EU Central Bank can cut off Greece. The US is not going to cut off USD exchanges; it jeopardizes its status as the world reserve currency. The US did not even cut off Russia, during the Ukraine escapades. The only two countries formally cut off from western banking transactions is North Korea and Iran. And Iran is not even cut off economically from Russia, China, or India. I think even South Korea gets oil from Iran.
The only two banks that Greece's banks will not be able to do business with is the EUCB and the IMF. In the short term, it won't be able to get loans from any Western bank, but that's only the short term.
you make a deal with the people who understand what's actually at stake.
Put Greece into economic slavery for at least a century? Its utterly implausible that Greece can "ever" payback the debt it owes to the EUCB/IMF at 100 cents to the Euro, without having a currency it can inflate. Germany did not continue to payoff its Versailles Treaty World War I debts after World War II.