FRANKFURT — No matter which way the Greek vote goes, the European Central Bank on Monday will face a series of agonizing decisions. Greece’s future in the eurozone may well depend on how far the central bank is willing to go to prop up struggling Greek banks and prevent a total economic collapse.  If Greeks vote yes — agreeing to accept unpopular dictates from other eurozone nations and international creditors in return for more aid — the central bank would have a much easier time justifying emergency loans and other steps to keep the banks from failing. No economy can function properly without banks; if they topple, so will the economy.  But if Greeks vote no, Mario Draghi, the president of the E.C.B., may be confronted with a difficult choice. The central bank’s rules would probably require it to stop providing cash to Greek banks. But Mr. Draghi might be tempted to find a way around those rules, because choking off financial support would thrust untold hardship upon ordinary Greeks and might send the country on its way out of the euro currency union.  The weak link in the 19-nation eurozone is struggling to tame its debt. On Tuesday, Greece missed an important payment to the International Monetary Fund.  Either way the situation is tricky, and there are no precedents to rely on.  “It’s fair to say we can expect a few surprises in the next few days,” said Nicolas Véron, a senior fellow at Bruegel, a research organization in Brussels. “Clearly, we are in uncharted territory.”  The E.C.B.’s Governing Council is expected to hold a conference call Monday to discuss Greek banks in light of the election results. If Greeks vote no — rejecting further austerity measures, even though that could mean no further bailout help — the central bank might focus its energy on minimizing the collateral damage elsewhere in the 19-nation eurozone. One way to do that would be to pump money into the bloc’s economy by stepping up the central bank’s purchase of government bonds, and other debt, from other eurozone countries.  But for Greece, its banks pose the clearest immediate danger. For months, they have depended on the E.C.B.’s emergency loans to compensate for withdrawals of money by Greeks who are worried that their government would be unable to reach a bailout agreement with its creditors.  The extent of that dependency became clear last week after the central bank decided to cap the emergency loans at about 89 billion euros, or about $99 billion. Because much of that credit line had already been used, the borrowing cap forced the government to close the banks before they ran completely out of money.  Under central bank rules, no emergency loans may be made to insolvent banks. If Greeks vote no, it will be hard for Mr. Draghi and the Governing Council to maintain the pretense that Greek banks are solvent. For one thing, the banks have large holdings of Greek government bonds, which have already plunged in value and would probably fall further.  Mujtaba Rahman, the Europe director for the Eurasia Group, a political risk consultancy, wrote in a briefing note on Friday that a no vote by Greeks would probably tilt the balance of opinion on the Governing Council in favor of members from Germany, Latvia and other eurozone countries that want to take a hard line with Greece.  International responses to the latest Greek proposal to resolve its financial crisis ranged from cautious to dismissive.  But the E.C.B. is treading carefully. It does not want to take the blame for any economic or humanitarian chaos that might ensue if Greek citizens choose to reject a deal with creditors.  Even if Greeks vote yes, banks may not reopen Tuesday as the government has promised. The banks have only about €1 billion, or $1.1 billion, on hand, Louka Katseli, the head of Greece’s banking association, said on Friday.  But a yes vote would improve the chances that Greece could negotiate a new aid package with the other eurozone countries and its other main creditor, the International Monetary Fund.  Those prospects could make it easier for the E.C.B. to justify an increase in emergency lending, perhaps allowing the banks to reopen soon, or at least continue dispensing limited amounts of cash. (Since last Monday’s bank closure, the daily A.T.M. withdrawal limit for people with Greek bank cards has been €60, or about $67.)  When the Greece government’s debt problems became evident during the financial crisis, leading to international bailouts of the country in 2010 and 2012, one big worry was that other European banks could be dragged down by losses on their Greek holdings.  By now, though, as European banks have sold off their Greek investments and new eurozone banking regulations have been put in place, that risk has been greatly reduced, according to the European Banking Federation, an industry trade group.  “European banks in recent years have significantly reduced their exposures to Greece, greatly limiting the risk of contagion through the banking system to other countries,” the British bank Barclays wrote in a briefing note on Friday.  From a small island to the capital in Athens, here is a glimpse into some of the lives of Greeks as their country struggles to repay billions in debt.  Barclays said that other euro countries had exposure to Greece amounting to only 3.5 percent of the eurozone’s gross domestic product and that exposure of European banks to Greece had fallen to less than one-tenth of that level.  But Barclays warned that the safeguards put in place the last five years were not “infallible.”  Even if the E.C.B. and other eurozone countries decide that Greece’s banks deserve a rescue, the process would be far from painless.  The central bank’s emergency loans would not be a permanent solution. The longer-term fix would probably need to come from a war chest called the European Stability Mechanism that the eurozone countries set up during the financial crisis to guard against future calamities.  That fund was used in 2012 and 2013 to lend €41 billion, or about $45.5 billion, to the Spanish government to help rebuild the assets of Spain’s banking system, which was teetering toward collapse. It was also used the next year to lend €9 billion, or about $10 billion, to Cyprus; some of those funds were used for its banks.  In the case of Cyprus, there were howls of protest when a eurozone bank bailout for the first time required some depositors to take “haircuts,” or losses on their money.  But two years later, as the new Cypriot government that came to power during the crisis had met the bailout conditions set by the eurozone and the I.M.F., that solution has been deemed largely successful.  If a yes vote prevails in Greece, and the country — perhaps with a new government — can come to terms with its creditors, a Cyprus-style bank bailout might be part of the package. That is the view of Daniel Gros, the director of the Centre for European Policy Studies, a research organization in Brussels.  “There would certainly have to be a quid pro quo,” Mr. Gros said, “and I’m almost certain that there would have to be some haircutting.”  Because of an editing error, an earlier version of this article misstated the amount of money that Greek banks have on hand. It is $1.1 billion, not $1.1 million.  Jack Ewing reported from Frankfurt and James Kanter from Brussels.
Unless the European Central Bank decides Greece’s banks deserve further support, they will probably collapse, taking the nation’s economy with them.