The worst case scenario for investors is that on Sunday night the re-run of the Greek election does not produce a coalition government both willing and able to implement the austerity plan Athens has already agreed on with the other 16 members of the euro zone.
The danger is that the Greek election would then immediately send out financial shock waves: powerful bouts of fear across the euro zone, and fear that if Greece is unable to cut its deficit, as agreed, then the EU-IMF will not be able to give Athens any more of the previously agreed bailout cash. The ECB would presumably also be unable to any longer help Greek banks.
The fear will then be that that Greek banks will collapse, and that in chaos Greece exits the euro zone, totally unable to pay the almost €400 billion it owes the rest of the world.
Immediately banks on the small island of Cyprus — which lent heavily to the Greeks — would throw themselves into the hands of their government. Cyprus would need an EU/IMF bailout. That’s a small, manageable problem.
Of far greater magnitude are the potential implications that a Greek exit would have in breaking the solidarity of the euro zone. If the Euro Dam has burst the fear would be, which country would be next?
Citizens across weaker nations might start withdrawing large amounts of cash: mass cash withdrawals to protect life savings that mushroom in to major runs on major banks.
In Italy, Prime Minister Mario Monti is pushing for a Europe-wide guarantee for bank deposits; in essence, for Europe to spread the responsibility for failed banks. But in Germany Angela Merkel refuses a banking union. Certainly not for many years.
The Spanish Prime Minister is rushing to get 'foreign' cash into his banking system to shore it up. Mariano Rajoy is anxious to break the link between problem Spanish banks — and Spanish sovereign debt.
Amid real fear that mass selling could erupt on all weaker sovereign debt markets, thus increasing the Spanish government's borrowing costs beyond the point of no return, Rajoy is pushing for all 17 euro zone nations to jointly issue government debt — creating one common interest rate — lower than what he pays now.
But Angela Merkel resolutely rejects that; German taxpayers don't want to pay more for their own government to borrow.
In fact, the Big Question is whether the Germans actually have a plan for Sunday night at all. Angela Merkel's public drive for long-term plans to centrally control individual national budgets rings very hollow for those that fear parts of Europe could — quite seriously — melt down.
That leaves only Mario Draghi, President of the ECB uniquely positioned with deep enough pockets to intervene and calm European markets next week.
But since Draghi explicitly warned Europe's politicians that he will not fill their policy vacuum, when it comes to the Greek election result Sunday — investors should be afraid, very afraid.
-By CNBC's Simon Hobbs