There are multiple levels of scary that can happen. One level is that the US loses status as world base currency as other countries move away from the petro-dollar. This will cause a spike in prices. Another possibility is hyper-inflation. We could even see the dollar finally breathe its last as its purchasing power goes to zero. Who really knows though. There are a lot of things that could happen, but they might be able to paper over the problems like they did in 2008. It won't last forever though.