I tend to be something of an innovation optimist, believing that most resource constraint problems are eventually solved through ingenuity and innovation, but there can be some hiccups in the process along the way. Here's an article looking at the airline industry, and trying to spin some scenarios of what would happen if it simply turns out that the commercial airline business is completely unsupportable
. Obviously, with fuel costs so high, it's become more and more difficult to keep airlines running (and it was never all that easy back when fuel costs were cheap). However, people seem to take for granted what cheap and readily available air travel allows. It touches on so many different businesses that it's hard to fathom how deep the eventual impact would be if air travel needs to be significantly curtailed in the future.
It's not just the obvious industries: airlines, tourism, etc. It would impact things like e-commerce companies that rely on cheap shipping. It would impact conferences. It could impact all sorts of industries when sales people can't as easily go visit customers. The more you think about it, the more industries you can find hurt by a decline in the availability of cheap air travel. Of course, there are other industries that would benefit as well, such as telecom companies and video conferencing firms.
Still, the optimist in me just sees the scenario as an opportunity for innovation. In fact, all of those other industries that would be hurt by a reduction in air travel would have it in their own best interests to help fund research and development into alternatives and improvements, so the funding for such innovation could come from many, many different places. But if it takes a while to figure out the problem -- and the airlines keep screwing things up themselves, there may be a rather unpleasant interim while everything shakes out.