They can still roll over debt, covering any debt that becomes due with new borrowing, which would not require increasing the total outstandingnationaldebt.
Just to recap the analysis in the previous post, over the past 20 years from FY1990 to FY2011 outstanding national and local government debt grew by JPY 500 trillion, 127.8 percent of GDP on a net basis (229.1 percent on gross), the highest among OECD countries by far.