When Groupon rejected a $6 billion buyout from Google in late 2010, the company clearly saw nothing but rosy skies. Generating nearly $2 billion in annual revenue, their prospective earnings at that point showed nothing but an uphill curve. Today, they’re likely singing a different tune. After peaking at a share value of $31.14 following their initial public offering in November, the stock has slid as low as $12.95 this April. That means there are a lot of early investors crossing their fingers for a rebound of a business model that probably won’t find a second life as rich as it’s first. Anyone…