Success that is not sustainable is not success.
>>and a lot if its downfall comes from how easy it is to copycat it.
No, I don't think so. The real (and perhaps the only) reason Groupon is not sustainable is because the fundamental assumption that the business model rests on turned out to be false. Let me explain.
The original idea was that Groupon would team up with a business and provide deep discounts to consumers to encourage them to try out that business. The assumption, which Groupon's sales folks used aggressively to push sales, was that a significant portion of those consumers would like the business so much that they would become repeat customers, thereby (in the long run) offsetting the cost of the original discount. In the end, the business would turn a profit.
Except it didn't work that way.
What ended up happening instead is that the vast majority of consumers never actually went back to the business. The reason is simple: while they could justify paying X dollars for the business's product or service just to try it out, they couldn't justify paying X times three or four. Because of this, most Groupon clients (the businesses) end up losing money, and never offer a second or third discount via GroupOn.
This is why GroupOn has such a huge number of sales reps: they need an ever increasing number of clients in order to postpone the inevitable sinking of the ship.