Don't underestimate the usefulness of having billions in stock at their disposal. If the valuation holds, they are probably going to start snapping up competitors and diversifying their business. Both would help insulate them from competitive pressure in their main niche.
Regarding the share valuation, most of the shares were placed with institutional investors (e.g. mutual funds, etc.). Institutional managers are less inclined to dump this early. It can happen, but it's less likely. That means Groupon has a small war chest to work with - not just cash, but the value of the unsold shares.
It's too early to say whether they are going to win or fail. A lot depends on what they do with their war chest.