It is the current doomsday scenario for Europe.

Greece’s bailout talks break down for good, and the country defaults. The European authorities sever life support to Greece’s banking sector, forcing the country to take drastic steps to stem an exodus of capital. Greece decides to drop the euro as its currency.

Greece’s unwinding sends shock waves through the global markets. Investors and policy makers have to quickly assess whether the storm is going to pass or gather strength.

Although Europe is better positioned to deal with a crisis than it was a few years ago, when Greece last teetered, there is simply no precedent for a country’s leaving the eurozone. And the big test may be only weeks away.

Relations between Greece and its lenders have descended into a bitter standoff. The impasse is increasing the chances that Greece and its creditors will fail to forge a deal by the end of the month, when a pile of debt comes due and its current bailout expires.