This was not like Skype, where it was actually successful and the engineers got screwed anyway - that's quite rare.
That a startup succeeds is quite rare. Just considering those cases though, I don't think ones where the employees also get screwed are rare at all. The groundwork for that is usually in place from day 1, with how shares in the company are split into classes.
For me it's been 100%: all three of the successful startups I've been involved with, all purchased by another company, did that transaction in a way that valued the common stock in employee options I owned at nothing. All the books were cooked until the company founders and, more importantly, the funding investors were paid all of the proceeds. And just to rub some extra salt in the wound there, the second also removed my name from the patent they were granted near the end of the process, to grease concerns that I'd expect more from the sale than nothing and could cause trouble with its licensing. (I signed those rights away in my employee contract, and all I really wanted was the little patent plaque)
The third laid me off, forced me to exercise my options to keep them, then valued the common stock at zero during the sale. That one's bonus fuck used some going out of business loopholes to cancel my COBRA policy with zero advance notice the week after the sale, as if they'd gone bankrupt and couldn't afford to administer the policy anymore. The company was sold for millions to Cisco; the engineers who built its technology lost their health insurance.
I've come to see these anecdotes as a pattern by design. Startups are not structured to make the employees happy if the company succeeds. They're setup so the majority share holder(s) get what they want. And there's a lot of rich assholes who will screw over anyone they can in that chain.