They vote is too late, they will default. Yves Smith over at NakedCapitalism lays it out nicely.
"We described in detail how the referendum scheduled in Greece for next Sunday, July 5, is a cynical exercise in democracy theater. The Greek people are being asked to vote on a (draft) proposal by Greece’s lenders to unlock €7.2 billion in funds, the last portion of the so-called “second bailout” agreed by the Greek government in 2012. Tsipras knew at the time he announced the referendum that the proposal expired on June 30; that was the known-well-in-advance final date for the bailout terms to be agreed if each and every one of the 18 Eurozone countries agreed. We said it was a no-brainer that they would not agree; in Germany as with some of the other countries, it would require parliamentary approval to accommodate Greece’s too-late request, and there was no reason for any of them to cut Greece slack when the government has plenty of opportunity to schedule the vote in time, so it actually would inform the government’s actions.
Instead, Tsipras has already taken the decision to miss the €1.6 billion IMF payment due June 30 and the €3.5 billion ECB payment that falls on July 20, while falsely telling Greek citizens that they have a say in this momentous choice."