If you have let's say enough revenue to support yourself, or at least to make your bank account stretch for years and years, but your valuation is $RIDICULOUS,

If you have let's say enough revenue to support yourself, or at least to make your bank account stretch for years and years, but your valuation is $RIDICULOUS, and then your valuation drops to $NOTRIDICULOUS, well... that sucks for your owners (including your employees, presumably), but your company stays alive and your employees stay employed. If you have no revenue and a high burn rate, then when your valuation drops you get no investors and can't pay your employees and the company folds. That said, I'm not sure I buy the idea that this boom is marked by a massive increase in companies with (significant) revenues. I mean, yes, Uber has revenues. Instagram didn't, Snapchat doesn't, Whatsapp had laughable revenues, etc. Uber is the most massive outlier of this particular boom. It is definitionally not typical.