Dept can be:

• repayed
• refused to repay (declaring bankrupcy)
• inflated.
  I vote for the third. Economists are wondering for 10 years why we don't have inflation. I think in some years, we will have. If the zero-interest-rate and the quantitative-easing-nrX don't help, the helicopter-money will have to come. (If nothing else helps to the economy, they will print even more money and give it to the people who will in fact spend it.)
  The USA also inflated its debt after the World War II.