Turns out every once in a while the gov picks up the tab and performs the reparations, while giving the residents an option to pay for the expenses during the next eg. 10 years or when selling their property. Some do refuse of course but mostly it works because the added value is quite high since it happens in hot areas where price/sqm is above avg. There are also estate investors buying bulk property in these old blocks knowing they will benefit from it, pushing retirees aside.
There are still plenty of troublesome condo blocks laying around without anybody touching them, but this might be a decent approach.
In inner city areas where wages make up a substantially smaller fraction of gross receipts in comparison wealthy suburbs, the excess burden of state and local sales taxes on workers is substantially higher. Replacing state and local sales tax with land value tax may reveal exurban sprawl was motivated by desire to avoid austerity rather than desire for more space, and that middle class really doesn't mind living a bit closer to cities.
It should be possible to design multi-story buildings which don't unexpectedly collapse in 21st century. Perhaps public sector urban building associations can construct and maintain high quality vertical apartment cores and elevators, but auction long term leaseholds which allow owners to privately renovate and mortgage improvements for their floor or unit similar to private condos. Partial local public ownership of building associations could then be used to assert leasehold fees are always sufficient to cover regular inspections and repairs. Partial public ownership could also be used to force a sale if owners have not occupied the property in several years, died, or emigrated in order to ensure increase housing availability.
We don't advocate for density. In fact, have specifically written against density as a metric. We argue for traditional development patterns, which look a lot more like historic Charleston or Savannah than Miami condos.
I guess if financial obligations exceed revenue (and assuming they can't borrow more), they go broke?