San Jose State University economist Jeff Hummel, in Econlib's feature article, predicts that the U.S. government will default on its debt. The other option he considers is that the federal government will monetize its debt. The problem with this second option, he points out, is that in a highly developed financial system such as ours, the federal government's gain from printing money, what economists call seigniorage, is quite small. Therefore, monetizing the debt simply wouldn't fill the bill, so to speak.
His closing lines:
Mises also argued that the mixed economy was unstable and that the dynamics of intervention would inevitably drive it towards socialism or laissez faire. But in this case, he was mistaken; a century of experience has taught us that the client-oriented, power-broker State is the gravity well toward which public choice drives both command and market economies. What will ultimately kill the welfare State is that its centerpiece, government-provided social insurance, is simultaneously above reproach and beyond salvation. Fully-funded systems could have survived, but politicians had little incentive to enact them, and much less incentive to impose the huge costs of converting from pay-as-you-go. Whether this inevitable collapse of social democracies will ultimately be a good or bad thing depends on what replaces them.