I don't know when but economics tells us that all economies go up and down. Greece will eventually go up but when that is, I have no idea. Could be next year or I could be long dead when it happens. Honestly, I think it will be after my lifetime.
As a member of the EU, Greece has certain protections. Whilst the political situation in Europe tends against bail out packages for failing nations, the economies of the memers of the Eurozone are interconnected and governments of the other states understand that a weak Greece will impact on their own economies and currencies.
Countries can fail financially just like people do. I think about the same think should happen to Greece that happens to people who can't afford to take care of financial problems. It sits to fester like a third rate citizen and then after about 7-10 years they should be able to fix themselves. If it's good enough for the people of the world, then it should be good enough for a government.
Greece will never be able to pay back what it owes, or supposedly owes, to its debtors. That isn't as much an indictment of Greece as it is of the whole debt system our world seems to run on. No country will ever be able to pay what it owes, including the United States, Canada, Great Britain, and all of the supposedly solvent countries.
Greece knew what it was doing when Germany bailed them out. They had no intentions to pay, only to have their problems soaked up into the rest of the European economy. And the rest of Europe was suffering at the time. Germany will eat all of the debt, because some how people who are responsible owe the people who are not.