Here's the crux of the matter: there are no alternatives. The US is a meta-country that drives the rest of the world. It's a proxy for the world.
Countries such as India and China have done very well in large part due to investments by Americans and American companies. Even during Japan's recession, the US economy helped keep Japan going. People and countries all over the world invest in the US dollar - Even today, when interest rates are at an all time low, T-Bills are still considered safe investments.
Will the economy continue to change and evolve? Of course. But America's place in the world economy is not likely to change in the near future.