Even with a super fuel, continued consumption of resources will cause our ecological debt to grow until we can no longer afford to pay it off. We will then have truly “broken the bank,” and need to be able to process raw material entirely by ourselves to form everything that we need and want. This would require a much more hefty energy source (such as nuclear fusion) along with technologies that could process mass at the atomic level (such as nanotechnology). For our consumption (and civilization) to continue uninterrupted these new sources of energy and means of processing materials would need to be available and operational when the biosphere crashed.
Suppose we were successful at living with a biosphere effectively reduced to microbes (or bioengineered life forms that are able to thrive). The net result of breaking the biological bank would be an expanding sphere of entirely artificial environments. Our growth of consumption would be limited by how fast we could reach and process raw materials, with the speed of expansion ultimately bounded by physics to the speed of light. Even under the most ideal circumstances, the rate of growth of consumption would likely peak no later than about 300 years from now, after which it would drop rapidly. We would be forced by the laws of Nature into a practically zero-growth condition.
The present geopolitical situation, relevant to the monetary debt faced by Americans, mirrors this same situation. Like countries at war, the main difference between what we started with in Nature, and what we will end with, is a vast amount of death and waste created in the conflict. In what is shaping up as a battle for influence in the Middle East, where much of the remaining (easily accessed) oil exists, the U.S. is attempting to do the equivalent of breaking the bank instead of reducing our spending, with potentially the same results. We will at best gain a few years of continued consumption, at a human cost already in excess of hundreds of thousands of lives. When the U.S. ceases to be a useful debtor, and the countries who hold our debt decide to either stop extending more or calling in what we owe, leaders like those currently in power may decide it's time to break the banks of those other countries, with even more tragic consequences.
Is getting more stuff really worth the harm so many of us are willing to do for it?