The government can pay its own debts as many times as it wants.
It can also dial the interest rate up and down virtually at will through QE or raising interest rates.
It actually makes less sense to think of government debt as debt and makes more sense to think of it mainly as a publicly run savings account.
The government can also push private sector loan interest rates up or down at will through the setting of the base rate.
Obviously governments can pay off debts as often as they want, and there was a time when that was common. But a government that runs up big debts and pays them by making the currency worthless soon has a hard time finding anyone willing to lend it money.
But sometimes they manage. Russia is notorious for defaulting on its debts (which isn’t the same thing as paying with devalued currency, but should be a lesson to future lenders), but they still manage to borrow money. But they do have to pay higher interest rates than other countries to make up for the higher risk of default.
As I said, it doesn't really make sense to think of the national debt as a debt. It's a government run savings account accommodating the private sector's desire to save money.
In the same way if maxlybbert printed maxlybbert dollars, spent them and then "borrowed" them back it wouldn't really be doing it because he actually needed them. He's providing a service.
I don’t really care whether it’s truly borrowing when a country sells bonds and promises to pay the bondholders back with interest. As long as the country feels it has an obligation to pay those bondholders, it has a temptation to pay them with devalued currency. Most countries don’t do that because they expect few people will buy bonds the next time the government wants to sell some.