"The fallout from a Greece failing would cause instability throught the world,.."
1. No it wouldn't. Greece represents only 2% of the EU's GDP and if it (economically) disappeared tomorrow there would be hardly any effect on the rest of the world outside Europe (but see below).
2. Greece has already failed. It has debts which are forecast to reach 200% of GDP under the new "deal" (up from about 180% at the moment). Little if any of this debt will ever be repaid. As part of the deal they are going to have to adopt measures which will further add to their woes making the chance of recovery even more remote.
Not for the first time the Euromaniacs emerge from their meeting after port and cigars, patting each other on the back, congratulating each other on reaching an "historic" (or did it read "hysterical"?) agreement. Not for the first time, before breaking out the bubbly, they seem to have overlooked the tiresome little task of running the terms of their latest largesse past the people who will be footing the bill .
This matter is by no means over. If it gets past the various hurdles it faces in the next few days and weeks (concurrence of the Greek and German parliaments as well as those of one or two other Eurozone members; concurrence of the IMF; legal challenges because the terms of the deal seem to break the Lisbon Treaty) the same problem will emerge again, probably before the end of the year and certainly within 12 months. This is because the Greeks may agree to the terms but have little intention or ability to implement them. It will not end until Greece is relieved of its debts, leaves the euro, reverts to its own currency and controls its own affairs. It can then revert to a declining economy (because they make no progress which sees growth and collect little in the way of taxes to finance services), a devaluing currency which reflects that economy (as all sensible currencies should) and resume their low tax, high spend economy of peasant farming with a smattering of tourism. But, as before they joined the euro, funded with their own money.
Of course the terror that the Euromaniacs fear is that a Grexit will see the beginning of the end for their ridiculously flawed single currency, at least in its current form. That's why they continue to refuse to face reality and solve the problem properly. It has nothing to do with saving Greece.