This depends on the structure of control in the companies. Anyone familiar with Facebook and Google knows that Zuckerberg pulled some fantastic manipulation of board seats and Brin and Page created a new class of voting shares that are 10x more powerful than regular shares. In such set-ups, the co-founders have permanent control of their companies without having to hold too many shares.

I imagine that many of the co-founders of the "unicorns" were smart enough to replicate Zuckerberg and Brin/Page and are subservient to no one.