I don't have the perception that the Bay Area startup scene is dying, but it's perhaps true that the Bay Area startup scene is dying. Basically, you can't raise a $3M seed round on "I went to (Stanford|Ivy League|other top college) and have an idea for a mobile app" anymore, nor can you raise follow-on rounds off anything but revenue growth. That means that the days where a couple 20-somethings could found a company, hire 10 people, and code by day while partying late into the night are gone.
Good riddance, IMHO.
The startup scene is still healthy, but is very different demographically. Some observations:
Average founders skew older - it's more 30- and 40-somethings that worked for a big tech company and cashed out a million or so in stock options, or had a previous startup exit. (The exception is crypto, which is largely financed through ICO now.)
B2B is ascendant over B2C, and many startups are financing the company with pre-sales from paying customers.
Team sizes are smaller, and many companies are using outsourced labor where they either open an office abroad for engineering, or they use Upwork etc. to find contractors.
Startups in general have gotten cheaper and leaner and are more focused on doing the work rather than living the dream.