In a theoretical sense, sure. In a real world sense, no way. These subsidies are not going to the pipeline company directly but to their consumers, who are large refining operations owned by even larger and more stable energy firms. So lets say that your super-volcano hits, closing down the BP refinery in Texas. You are saying that the tax incentive now becomes worthless. In fact, BP still gets that tax incentive, and they will just take it out of their other operations. The default risk for these firms is negligible (made even more so by the fact that closing these firms would likely be considered contrary to national security in addition to the too big to fail component). And since the tax break is over a series of years, even a bad year or a bad several years (ie. lets say we all stop using gas next year but go back to it in 2 years) would still not eliminate the tax credit.