Like the old joke about only having to outrun the other guy but not the bear, the US is only at risk if it ends up less stable than somewhere else and doesn't manage to trip them up on the way down. It's still hard to see any more realistic alternative; the EU is struggling with the same crisis, and the Chinese government doesn't even want its currency externalised.

Unfortunately not. The US is the tallest midget for the time being, and that’s unlikely to change in the coming decades.