My point is, I seriously doubt the CTO was forced out or left because he thought his stock was worthless. He is most likely leaving for any of the million other reasons people leave companies every day.
When this happens it so harmful to the little guy and all of the employees stuck in the middle.
The idea that we're in a bubble on the cusp of collapse has been building over the past year, spiking when the feds raised interest rates, but there's no concrete evidence of a bubble popping. Yet.
Get worried when we see (multiple) high-level execs also resigning from Facebook/Twitter/etc. Especially if it's of their own accord...
http://recode.net/2016/01/24/twitter-ceo-jack-dorsey-confirm...
https://news.ycombinator.com/item?id=2231352
So the majority of people called a tech bubble, unlike your claim that most people are "permabulls", and then there was a period of great growth and prosperity. There have been plenty of people predicting gloom and doom to happen before now and none of them are admitting they were wrong. So basically it's gone down exactly the opposite as you've described.
Eventually, the naysayers will, to an extent, be right. But it's ridiculous to act like financial market movements are obvious and we should all predict it perfectly. It's even ridiculous to act like a few resignations is indicative of a bubble popping. The strongest evidence that a bubble does not exist is all these weaker companies struggling, because in an actual bubble they would be propped up by the relentless speculation. Yet people point to failed companies as proof there's a bubble, even while many tech companies are doing great.
Either way, financial markets are very difficult to predict, unless you count predicting the same direction for years and waiting for it to be right. So stop acting like it's easy and obvious. If you really feel so strongly, put your net worth into shorting tech stocks and make a ton of money.
Whether or not this describes Silicon Valley is a further question, but it sounds like based on your standard, you wouldn't give credit to a naysayer even if it did.
More likely, at some point we'll see a bad year or two, some hiring freezes and layoffs here and there, and people point to that as a bubble collapse that they "knew all along", even though they "knew" it during times when the sector grew more than it eventually receded.
In real bubbles, you see a insane amount of growth based on pure speculation, followed by a massive collapse. The justification for a "bubble" so far has been based on incredibly silly things like the engineers making 80% of what lawyers make or private valuations being high (which only affects a small number of people and is often inflated by things like liquidation preference incentivizing it to sound artificially high despite a significantly lower risk).
Companies like Zynga, Groupon, Living Social, Homejoy, Twitter and Yahoo struggling during a so-called "bubble" is not insane growth, it's proof the market has maintained skepticism over the years. And a few more unicorns falling over won't be a massive collapse either.
Every market has downturns. Not every downturn is a bubble. And an actual "bubble" existence hasn't been proven true despite repeated insistences for 5 years, and I highly doubt it will start now, unless we uncover massive, massive fraud.
Shorting too early is an insane money losing proposition.