Predictions of the demise of the US have been made by a number of people, and there are good reasons to think there might be something into them. For one thing, the US gained its superiority as a result of historical accident - mainly because Europeans were at each other's throats for the first half of the 20th century. That allowed to the US to get rich by selling them weapons, and also weakened Europe - which put the US at a relatively strong position which it was able to maintain mainly due to the Soviet "threat."
But there is no reason why the effects of this historical accident should continue indefinitely. Although the US enjoys military superiority, otherwise it is a pretty backward society, socially, culturally and politically - basically a third world society with the first world military.
The problem with military superiority is that it works only to a certain point - namely, until the low-tech combatants gain the means to harm their high-tech opponents. At that time, technological superiority is overkill - a US-ser killed with a strategically planted primitive explosive device is just as dead as a non-US-ser killed with a satellite-guided cruise missile.
So military tech superiority works mainly as a deterrent - "do not attack us, because we have better fighting machines." But once hostilities erupt, the attacked people will use any means to harm their attackers - and there is enough "low-tech" weapons available to do a really big harm with these, as 9/11 clearly demonstrated.
But beside their military-tech superiority - which is a dubious way of exercising imperial control anyway - the Us has very little other means of making other countries to follow it lead, either voluntarily or by coercion. So its demise is a probable outcome.
Wojtek