It all depends on population problems...if the population growth halts and reverses (hopefully by choice instead of by AIDS and other horrors) there will be such better times ahead for everyone. If not, maybe we'll adapt and maybe not.   

Good scenario:
We won't need U.S. power. Goody. We can keep our prosperity and others can have theirs.

I think we won't need roads because we will have aerocars using magnetic levitation or something. Just float above the surface and if an obstacle arises, zoom over it.

We won't need big cities. Population will be better distributed, like back to South Dakota. Fuel will be non-existant because we will harness the wind and sun and turn sewage into electricity. Wait and see.

Food will be more local, if we can ever gather our wits together about this. We won't look for the cheapest food, but the healthiest (we are well on our way to this now that we have a substantial working and middle class).

There will be more village dairies and gardens and orchards like in bygone days. We will wonder why in the world we bought food from Chile and South Africa.

We will know much more about people's nutritional needs and taylor nutrition accordingly. There will be much much less obesity, diabetes, heart problems, and all the drugs they dose people with.

All this information and knowledge will spread via the internet rapidly..good science will be done and applied.

Once tyrants tremble and quit oppressing people, all sorts of stuff can be delivered to poor people, if necessary, like emergency food in famines, vaccines etc...what keeps it from them now is often having to fight their way in. Through micro loans etc. poverty can be eliminated.

So if the world gets better it won't need US power. If it gets worse, there are way worse scenarios than the US taking charge. Remember these words: by our sons in servile chains..by Robert Burns. Think of it. Whoever else would be in charge might not be benevolent.

mg