From what I read about Detroit, once businesses started shrinking or leaving the tax base shrank.
The city was unable to cut down on services and spending, so it raised taxes on everyone remaining and the squeeze of more tax and worse QoL made people leave even faster.
I'd love to hear if anyone has examples of a city's tax revenue shrinking at least ~20% in a couple years where the city correctly adjusts their services and scope to match, without facing some runaway decline or lost decade.
Open to discussion on this.
EDIT:
Thinking aloud, maybe the people leaving Detroit due to loss of services/QoL were simply in the parts that Detroit was abandoning to make ends meet?
That's the question isn't it? San Francisco has by far the highest per-capita city budget in the country. It spends more on homeless services in a year than most cities of similar size spend on everything. The city is simply addicted to spending money, and looking at the deterioration of street conditions, increase in homelessness and addiction, increase in property crime and more, they are clearly not getting its worth.
Theoretically could the city make do with a 30% budget cut year over year? It absolutely could. Columbus, Jacksonville, Indianapolis, Fort Worth, Memphis, and even San Jose and San Diego somehow survive on 1/5 - 1/10 the money despite supporting similar sized populations. It remains to be seen whether San Francisco can make the correct cuts and not drive away the remaining tax generating citizens and companies.
Will the millions of people clamoring to move into SF or any dense US city turn into a negative number?
The people on the sidelines will definitely provide a floor to the prices of the homes.
Home prices aside though the loss of the lucrative office workers buying lunch and renting offices will decrease tax revenue.
Unless someone has any examples of a city that has navigated a downsizing well I do believe the QoL in 5 years will be worse than today's (provided we don't see an epic return to office).
The question for people invested in the region is: "how much would demand from sideline people for these properties change if QoL was worse?"
EDIT: Reworded the heck out of this
EDIT: again
I lived in SF for 19 years, moved to London (family reasons, elderly parents with health issues) and are planning to return to the US. My wife put an absolute veto on returning to SF itself because of how dire the law and order situation has become.
Sad to say, but the city really needs a 1990s vintage Rudy Giuliani to clean house. Otherwise what it will get is Bernie Goetz (yes, I know, I am showing my age with my references). It seems unthinkable today, but in the 1950s and 60s SF was actually a fairly right-wing city, all mayors from 1912 to 1964 were Republicans.
My understanding is that prior to the "Southern Strategy" (https://en.wikipedia.org/wiki/Southern_strategy) of the 1960s, the Democratic Party was largely right wing, and the Republican Party was largely left wing.
So San Francisco flipping from Republican to Democrat aligns pretty much squarely with the change in politics of the parties due to the Southern Strategy.
This implies that in fact, San Francisco has always been fairly left-wing.