A lot depends on whether or not Syriza wins in the next Greek elections. If they do, it will be tough, as Syriza is going to try to negotiate less austerity for the Greeks, which the bigger players in the union may or may not agree to in return for the preservation of the currency. If Syriza gives in and agrees to anything like the current austerity terms, they will be discredited, and will probably face political annihilation at the next election, which gives them even more incentive to not do so. Europe would have to negotiate with a party that is both rather unreasonable and has a gun to its head. If New Democracy wins enough of the vote, they'll likely just form a pro-austerity coalition with PASOK, and the euro will survive. If we get another mixed outcome like last time, then New Democracy is going to have to try and arrange a coalition with PASOK, the Democratic Left, and Syriza - this totally failed last time around, but perhaps could work out due to the peoples natural reluctance to hold a third election.
It would look rather bizarre to have a center right party lead a coalition of Socialists and post-Communist, but the only other right wing parties in parliament are the Independent Greeks, who are anti-austerity and would more likely form a part of a Syriza coalition than anything else, and Golden Dawn, who have vague neo-Nazi associations (using "Roman" i.e. Nazi salutes, also having a party symbol claimed to be something "Hellenic" but just happening to resemble a Swastika), and are therefore obviously anathema to every other party in parliament. There are, of course, the Greek Communists, but they refuse to participate in government, and unlike most other large European "Communist" parties, which are basically just trumped up social democrats i.e. eurocommunists, the Greek Communists are actually a hardline neo-Stalinist party. Syriza is actually the result of a split between the Eurocommunists and the hardliners that occurred after the fall of the Soviet Union - hardliners staying in the Communist party and Eurocommunists going to Syriza. Syriza and the Communists hate each other due to this historical enmity, and the right obviously isn't going to take them into government, so they're not going to be part of any coalition. The vote for the Communists + Golden Dawn is basically a threshold that any coalition of the other parties has to exceed in order to hope to form a sensible government.
