Uhhh doesn't a VC need to close out their position eventually? And mark a return on their fund? If you take VC money you can't be private forever, you need to be acquired or go public.
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.