I don't believe America will come to an end, at least not in our foreseeable future. We will go through many changes. We really need to adapt because of the globalization all the countries have gone through in the past 2 decades.
First we need to define what is America. I believe that America is about opportunities, democracy, organization, has law and order, a basic Constitution and several other factors for which to define this country I won't delve into for now.
So long as most of those qualities are in place, America isn't going anywhere.
We may go through outsourcing, challenging educational standards, drug wars and addictions, international policing, humanity issues and some other things like that, but the backbone of this country is still the same as it has been for the past couple hundred years. FREEDOM of speech, universal rights for all registered citizens, an organized honest financial system (for the most part ><) an the ability to utilize all the resources it takes to start from nothing in this country and literally overnight to create honest fortunes.
Any other country will have systems in place we wouldn't like, just like we have some here we don't like, (ie monitoring of our emails etc) but for fu*%& sake, there have to be some concessions on our part because of the complexity of the world today and the unbelievable amount of despots out there wanting to promote chaos and disorder, so we will need some sacrifices along the way to ensure our forefathers dream will live on for as long as we work to make it to.
Ok enough rambling