The world economy is intertwined, the US economy is dependent on the world economy and vice versa. Naturally the world economy would suffer greatly if the US economy failed, but it would eventually recover and other economies would fill the vacuum.
This was what I was gonna say. If Europe, China, or the US economy fail the effects will be felt worldwide. But things will recover. This is part of the issue today, Every region is messing with their currencies. Trying to force infinite economic growth every quarter.