[vannevar]

Groupon went public, and their stock went from $26/share to $4. If the same thing happens to Uber in a down round, that's pretty much the definition of collapse.

[danielweber]

Without saying whether I think such a thing is likely, Uber compensates significantly with stock, and they cannot retain talent if the trust in the cashout goes away.

[user5994461]

They give ISO which are worthless and might fire back for a lot of employees.

They won't be able to retain talent when the talent will figure out they can't get the stock that was wrongly promised.