Oh, I doubt we'll see the end of the human race. As somebody once said "every generation thinks they will see the end of the world". Certainly its possible, but more likely I think we'll see some pretty big changes happen in the status quo of the current major nations.
And, of course empires do come and go. And in long run - from the perspective of whats best for the human race as a whole, and all the other species on the planet - the USA *needs* to collapse back to the stone ages.
But, from a selfish standpoint -- I sure as hell don't want it to happen during my lifetime, I don't think it will be very fun!
It would seem like the USA could just throttle back and join the world community, become more self sufficient and stop meddling with the rest of the nations. However - I think our ego's are too large - I think that we can't live with just being another country like a Switzerland, or even a Canada. I think if we can't be #1 in consumption and military power -- then by god we'll go down in flames and take the rest of the world with us!