The phrase "cities without commercial on street level and residential above, cities where you need to own a car" is adding a condition onto "this is how cities die" to say that the original prediction doesn't apply to SF. Because SF has "commercial on street level and residential above" and you don't "need to own a car", people in the rest of the city depend less on the downtown. While downtown may be abandoned, it's not heart of the rest of the city.
At least that's what Terretta is saying. I haven't even visited SF in over a decade, so I don't know what its current situation is like.
Grandparent said "this is how cities die" related to remote working and emptying the downtown core - as is happening SF.
You then said "This is how cities -- cities without commercial on street level and residential above, cities where you need to own a car -- die."
The topic is San Francisco. So am I to read your comment as completely unrelated to the topic at hand?