After the bomb was dropped on Hiroshima, America didn't come in and "fix" the city. It helped Japan to build a new city. Hiroshima had to start over.
That's what will happen this time to. And what gets built probably won't be America anymore. Most nations that get built from scratch don't turn into America after all.
I can't say this often enough: The full federal debt is not $19 trillion. In addition to the declared debt, there is also an enormous obligation to pay retiring workers their Social Security checks. And there is an enormous obligation to deliver healthcare to older Americans under Medicare. These 2 obligations dwarf the rest of the federal debt, elevating it to a staggering $225 trillion. That's about $700,000 per citizen, a figure so high as to be beyond any possible hope of being payable. It would take more than the average American earns just pay the interest on it.
Yet, the other option, defaulting, is horrifying beyond words. It would bring the country to a halt, forcing nearly everybody to live off of the money in their houses and the provisions they stored away. And you can guess how long that will sustain them.
What happens in a nation like this when 300 million people are effectively destitute, without any government to provide benefits? Forget about assistance from abroad, even if such a thing were to be offered. It would not be timely, and when the United States goes down the rest of the world will as well.
Folks who survive for 6 months will probably make it through, but I doubt very many will manage to do so. We're too urbanized, too far from food sources... too dependent on gasoline for the distribution of almost everything.