The link above describes proposals to clear large sections of rust-belt cities in North America.
Cities in the U.S. were always provisional and developed in the process of capitalistic creative-destruction, as evidenced by the slum clearance campaigns of the early 20th century and up to the present time. In the "shrinking city" case, instead of a rapid change in function, or at least form, financed by private enterprise, various levels of government would have to step in to speed up the re-creation of the urban shape.
The urban experience at the personal level was always one of embodied and existential fragmentation. Cites are, and always have been, made up of various neighborhoods with their own character. The proposal to create urban enclaves separated by green spaces would further actualize on the cityscape what was, at least somewhat, already true.
If peak oil comes to pass, perhaps even some suburbs would have to be abandoned. In any case, whether rust-belt cities shrink or outer suburbs are abandoned, there would have to be a rationalization of land use so as to move food production closer, and even into, cities. Already, there are urban residents who now raise a few chickens in their backyards. Hopefully, we will not return to thousands of horses and cows inhabiting cities (it was messy!), but it makes little sense to ship produce thousands of miles. The opening of urban space would facilitate this trend of peri-urban food production.
The "spaces of destruction" would be ready for "neighborhood," and green-space and food-space development. Instead of the domestication of the natural environment, we might have the reverse process of the naturalization of the urban environment.
This line of thinking reminds me of Pyotr Kropotkin, anarchist and geographer, who, in Fields, Factories and Workshops, said,
"The two sister arts of agriculture and industry were not always so estranged from one another as they are now. There was a time, and that time is not so far back, when both were thoroughly combined; the villages were then the seats of a variety of industries, and the artisans in the cities did not abandon agriculture; many towns were nothing else but industrial villages."
Prince Pyotr was perhaps also a geographic prophet.
Are we rapidly moving back (and forward) to this--open, green, farming urban areas?