Universities are institutions made of people. If SF becomes to expensive for those people to work and study in, they'll face the same problem of housing costs. And universities rise and fall over time: a great CS department one decade might slip down the ratings the next.

There are many places on Earth with nice weather and scenery (depending on taste). There are many cities with great night life for younger people, or good schools for families. None of these things are unique selling points intrinsically required for a tech hub. And if remote work becomes the norm (and yes I know all the arguments for and against) you can live in your dream town with the right mixture of scenery/weather/nightclubs/schools without paying the premium.

The one thing SF has is inertia : tech happens there because it happens there. But Detroit used to have inertia, too.