the US makes up about 35% of the world's consumption of consumer goods. We import so much from so many countries, including China, that they would have a harder economic time than we would if they cut off our credit.
Honestly, interest rates would go through the roof, driving more investment into the US. The Fed will probably go into quantative easing, devaluing the Dollar, making goods more expensive but debt repayment cheaper. Remember, inflation is good for the debtor and bad for the creditor.
There are 3 countries in the world that will never fail do to their consumptive power. Germany, China and the US. I would be more worried about a shift from the Petro-Dollar to a Petro-Euro, which will never hapen because of the relationship between euroean powers and Israel.