I doubt there's any way to get a good answer to this, at least not in detail. A big part of the reason it didn't happen is because no-one had a clear idea what the consequences would be, or even how it could be practically done, and really didn't want to find out. I suspect some of the medium-to-long term results would have been:
A domino effect (starting with Italy) of capital flight, followed by Cyprus-style capital controls, followed by a reversion to national currencies;
A collapse of some of Germany's largest banks as their Greek debt holdings evaporate, followed shortly by a collapse of the German government;
Europe plunged into a recession that makes 2008 look mild, which combined with China's slowdown will push the global economy into full depression;
A reduction in the number of Syrian, Iraqi and Afghan refugees coming to Europe as it becomes less attractive, but a large increase in the flow of Greeks northwards as their country implodes, with no money for imports and locals paid in a rapidly inflating currency that's not worth the paper it's printed on.
Over the next few years, a further rise of nationalist/populist governments pushing a sovereignty agenda that sees the EU break up (incidentally making Cameron's renegotiation irrelevant, assuming he even bothers to try it).
Basically, I'm not seeing an up-side here.