Where does this view of "its downtown or suburbs" come from? Cities have urban cores surrounding the immediate downtown. At least around here.
Well, for some cities, even if the desirability of living in the city instead of the 'burbs goes up, the number of people in the city can't go up too much.
There will be economic pressure to fill all the abandoned houses (some cities have very few) and to fill up bedrooms in houses or apartments that are under-occupied. Construction on abandoned lots can absorb some increase in demand, and to some degree the construction of additional living space on existing lots.
But cities can absorb only so much increase in density, before people will be literally forced to live outside the city for lack of an available home in the city.