“we will have trillions of dollars worth of obsolete infrastructure whose financing costs will still have to be paid ”
Not an issue in New York City. The last major subway line was completed in 1940. The bonds have long since been paid off. Fewer commuters means that we might not have to build another half dozen lines to handle the still booming population. (NYC has about 1.3 million more people today than it did in 1940. That is roughly the population of Dallas.)