The most likely outcome is that Silicon Valley once again broadens geographically, rather than dies. It has been doing that in bursts basically since HP was founded in 1939.

The YIMBY forces are not going to succeed in fundamentally changing San Francisco. They've been failing at that for two decades. Instead, the money and start-ups will push further out. When people talk about Silicon Valley today, they mean a much larger geographic area than what that would have meant just 30 years ago. 30 years from now, the name will have grown to encompass a far larger area.