If the cost to government of servicing its debts is lower than the tax income extracted from the private sector, they can deleverage their debts, given sufficient time. (Assuming the government is able to continue issuing the required debt at sufficiently low rates of interest.)
In the days of yore, when there was a gold standard of some sort, this would be a protracted and painful process to pull off successfully. But it was done.
Fortunately, today, the government doesn't have to rely on the free market to supply the necessary credit (as in the good old days). It can issue credit to itself, in effectively unlimited quantities (but in reality limited by the credulity of the market). In so doing, it is able to suppress the interest rate that it must pay (and also receives the interest paid back as income - so the true cost of debt service is effectively 0%), ensuring that it is able to get the credit on economic terms.
The only way the system of today cannot be deleveraged in this way, more rapidly and painlessly than in past examples, is if the free market significantly rejects the governments currency in payment for goods/services, requiring the government to issue ever-larger quantities of debt to itself in order to cover its expenditures on goods/services, outpacing its ability to service the debts from the tax income it can expect to receive from its citizens over the requisite timeframe. The holders of existing debt instruments may also choose to liquidate and flood the market with these assets, outrunning the governments ability and/or willingness to absorb it all - exceeding their ability to contain the interest rate required in the market and thereby blowing their scheme to deleverage out of the water. Oh my!
It could never happen here!