1. Political dimension: A Greece exit, i.e a return to the drachma, a default on its EUR denominated debt and more importantly a return back to monetary and fiscal sovereignty will - after probably a difficult period of 12-18 months - trigger a huge economic rebound (as it was the case for example in EU in Island). As a result, anti-EU parties across Europe will gain significant credibility and the "farce" of Troika' forced auterity will be totaly discredited. So politically this is simply not possible for the Troika - the current game-theory driven negotiation are only a staged act for the media/population. If markets could correct a bit more before the final outcome, the Troika/Grece Gov. could be even more happy has their "TV-novela" will be more credible and they will on top of that be considered as "hero" once they find a deal and market rebound as a results.
2. Financial dimension: just look at this charts, which is Greece loans to deposit ratio - this leveraging is made mostly with ELA (Emergency Liquidity Assistance)....- so if they default or exit...this is the double whammy for EU central banks that need to honor payment via Target. That s also explain why the ECB is keen to save Greece from default and exit illustrated by EUR 90bn in loan from ECB vs EUR 44bn in assets.
