I suspect the “lost population” of most of those cities didn’t move very far. They might not live within the city limits any more, but they’re still in the suburban metropolitan area, in most instances.
None of the cities listed in the example are what I would call thriving, but I wouldn’t call them dead, either. New Orleans may never be the city it was in the 19th and early 20th century, but Katrina cleaned out a lot of the dead wood and things are actually moving in a somewhat positive direction now—admittedly with a long, long way to go. Galveston took a hard knock, but it’s not going anywhere. He has a better argument with Detroit and Cleveland.
Actually for the snowbelt cities the lost population has moved very far away, down to the sunbelt. There’s been a big “seeking warmth” trend to the population in the last 10 to 15 years, most snowbelt states have lost population and most sunbelters have gained.
Now the sunbelt cities on the list you’re probably right, the people are probably still fairly close.