Maybe calling every critic in your town names and letting QoL go to absolute crap is the real driver of movement.
The crime/urban blight angle is a red-herring; It implies that there was anytime in the last 30 years that New York/San Francisco was anywhere nearly comparable to a city like Tokyo.
Manhattan is already seeing a net influx in people moving back into the city.[1]
[1] https://www.sfchronicle.com/sf/article/sf-covid-recovery-nyc...
The comparison to Detroit seems apt. When the automakers scaled down, there was no "Plan B" and the city leaders were too incompetent/corrupt to actually lead.
The "worst" scenario for SF in the event of a work-from-home sea change is that the COL regresses to a "normal" level for a city with its (impressive) amenities and natural environment, and it stops being propped up due to proximity of so many fatcat tech workers.
"Worst" is in quotation marks for a reason, because this feels like a highly desirable outcome for everybody (except for the fatcat real estate owners doing the rent seeking).