If the valuation didn't change, and the common stock is fairly priced, then we should stop calling the valuation $70B. Under that model, Uber was never worth $70B.
It's expected that common shares are worth less than preferred shares. After all, the preferred shares could be paid out at value in, e.g. in the event that the company is sold for far less than the current valuation, and the common shares would be worthless.
Probably not. The strike is likely at a much larger discount.
There is a thriving, if shallow, secondary market for the private stock, common or preferred, of companies like Uber.