If I recall correctly, groupon raised something like $100 million immediately after they rejected Google's offer.

At the time, I remember reading that almost the entirety of the investment went to buy out early investors.

So it looks like Mason got the best of both worlds: he got the cash out a substantial number of shares and then hang on for the IPO upside.

You also forget to mention that the Google deal was contingent upon due diligence, which now, in hindsight, may not have even successfully gone through.