When a state fails or falters, all reversion is to the people. The UN and NATO could conceivably have roles in the territories of the United States. The people of each of the several states, however, would experience full reversion of power. While the Hollywood line is one of power reverting to persons with the nicest suits, most elaborate sound stages, most palatable lies and best special effects team: the truth founded on most ancient law is that if a state dissolves or falters the power reverts to the people. The peoples' right to self-preservation has never been the subject of federal legislation and such right was never delegated to Congress.
The trusteeship of the United States government over the territories ceded to the United States by the several states ceased when states were formed. There may be some "nuances" introduced with respect to states formed after the Civil War started.
The Hollywood myth is: "Those guys in the fancy suits have all of the power cos those fancy suits are really groovy."
The truth is ancient: all power reverts to the people when a state fails or is dissolved. In the event of demise of the United States of America, the power reverts to the people of each of the several states which formed the American confederacy. Similarly, if one's landscaper died or had to leave town to visit a sick relative: you can mow your own grass.