The research at Los Alamos that Geoffrey West has summarized most recently in his book Scale demonstrates different dynamics are at work. Creatures and companies grow and age and die. Cities are a completely different construct. Rome and Londinium are both still large and influential. Two particularly stark demonstrations of this effect are Hiroshima and Nagasaki both of which were wiped off the map with nukes yet in roughly 30 years were back to being thriving urban conurbations. Times change, but influence remains more consistent than most expect. The startup scenes in Detroit and Cleveland are other examples of boom towns that were written off yet remain significant contributors.

Sure, there is still innovation coming out of Detroit and Cleveland, but I still think if SF/SV became like one of those cities that would qualify as "dying" to a lot of people who currently live there.