When you get your hours cut back you don't pay the gym bill and the cable bill before the mortgage and then say the cutback cost you your home. You pay the most important bill first and do without the gym and cable and cover the mortgage. The same applies here. Paying for unessential stuff before the debt payment and then claiming the cuts led to not servicing the debt. It's irresponsible spending. Money is still coming in, pay the debt first. Common sense.
Ultimately what happens to the unpaid domestically held public debt is that we effectively kick the public debt can on down the road once again. At some point this just devalues the dollar. Heck, if we do it long enough we will be able to pay off existing debt quite easily because the dollar will be so devalued that a cup of coffee will be a trillion dollars.
If we want to avoid this kind of mess then the ONLY options are to reduce spending on "stuff" or increase tax revenue to the point where we can handle all of the obligations. There are a few ways to increase tax revenue but that's another issue entirely.