Not entirely true, the other option is that other people buy the VCs out of their stake in the private market. In sharply profitable companies, a company could

Not entirely true, the other option is that other people buy the VCs out of their stake in the private market. In sharply profitable companies, a company could in theory buy itself back from its own investors without needing to be either acquired (it acquires itself, essentially) or doing an IPO. Of course, your company actually has to be making money to do this. Which for most unicorns is something of a problem. All investment is essentially debt. At some point either someone else chooses to hold it at a value that is mutually agreed on, or the company buys itself back.