Greece has missed the payment to IMF and survived without much of any immediate consequence (though IMF will withhold further funding to Greece), however a payment miss to ECB might open up Pandora's Box for Greece, which might lead to Grexit.
Greece is due to pay, European Central Bank (ECB) € 3.5 billion on July 20th. As of latest information, it seems Greek government doesn't possess the money to pay back.
European Central Bank (ECB) has lent Greek banks € 89 billion in emergency funding, which risks withdrawal if Greek government defaults on its commitments.
With ELA from ECB gone, banks are inevitable to fail as bank run will intensify.
With all liquidity being sucked out, Greek government will have no option but to move to a parallel currency or the New Drachma.
However, such a progress or move to a currency will be a very difficult choice to make and even its made it might take almost a year to shift to such arrangements.
