It's not going to happen before 2018. The US economy is actually doing quite well right now. I could see it happening eventually but I think you are safe with your fiat for a good while. These banks have a lot of fight in them and they're gonna do whatever it takes to keep things afloat. Greed is a powerful force.
There are a lot more factors to a dollar than just an economy and how good it looks on the outside.
While I'm not going to say that the US is in a state of collapse and everything is just going to be getting worse, it really is starting to dramatically degrade on the inside and there are a lot of divisions within that country that can escalate very quickly if people start to shove. If something like that happens, everyone takes a brutal hit and the US Dollar won't be viewed as strong if their citizens start fighting each other in the streets. Opens up a lot of other doors for things to happen.