When the US announces it will not honor it's debt, a third party occupies the US in order to secure it's assets for the creditors of the US.
Some believe the third party will be the UN, others say NATO, still others say it will be the actual Chicoms, who will stage in Mexico (with the approval of Mexico in return for a cut of the spoils, namely lost territory along their border) and from there they will invade in a multi-pronged attack in an attempt to secure both California (the actual breadbasket of America) and the refineries along the Gulf coast.
I think that scenario is unlikely, but not impossible.
Assets could be sold off to pay the debt. The federal government owns most of the land in the West and much of it in the East.