This whole saga exposes the pitiful state of the media in informing its consumers: Sensational headlines (generalisation), Zero details.
The talks to reach agreement were abandoned after the last Greek proposal where the situation was :
the primary budget surplus till 2022 was agree upon,but the method on how the Greek govt would get to those budget surpluses was not deemed credible by 'imf ecb eec' ('troika') ie Greece suggested corporate tax rise from 26% to 29%/troika only wanted it rise to 28%, Greece suggested a one-off 1% tax on corporations of 12% of net income troika NO,,Greece wanted not to decrease pension expenditure as much as trioka wanted , Greece did not increase VAT/consumption tax to degree troika wanted.
So negotiations were abandoned and a bailout which would have been be used primarily, if not exclusively, to pay Greece's creditors - the IMF ECB and the other member states of the eurozone
There is no basis in law or under european treaties to exclude someone from EURO peremtorily ,the Greek govt are not putting a no vote forward as leaving the euro, but a refusal to accept the diktats of the troika. ( but of course it would not be the first time government's did not adhere to the internation treaties they signed when it suited them when they are defending the interests of capitalists.)