The "no" vote in its referendum last Sunday seems to have accelerated the momentum towards a Greek exit for the euro. While there is plenty of room to second-guess the negotiating strategy, I think the Syriza government and Greek voters were right to reject continuing on the same policy path. If they are forced out of the euro (which looks likely), it will be traumatic and disruptive, but the experience of Argentina in 2002 suggests a fairly quick rebound (from a very low starting point) is possible.
Ultimately, this may be worse for the rest of Europe - not only does it open up the possibility of future crises by demonstrating the reversibility of the euro, it also demonstrates a fundamental lack of solidarity: the "ever closer union" isn't really that close (see Dani Rodrik and Peter Eavis).
Some of Europe's leaders seem recognize this; the main stumbling block in the last-ditch negotiations appears to be on whether some of Greece's debts will be written off (i.e., "restructuring" or "haircut"). The IMF has publicly said that Greece's debt are not sustainable (debt writedowns are part of standard IMF interventions), and the US is urging a writedown.
Politically, it is easy to see why this is a nonstarter in many of the creditor countries. Some "leadership" is badly needed, particularly in Germany, and doesn't appear to be forthcoming: in the Times, Bruce Ackerman calls out Germany's "failure of vision." Clive Crook argues that the Greeks are being deliberately pushed out. Eduardo Porter notes that Germany seems to be forgetting that it has been a beneficiary of debt relief (see also Thomas Piketty). The German stubbornness may be more than just politics - Simon Wren-Lewis argues part of the problem is that they (naturally) do not want to acknowledge the failure of their economic ideology.
Last minute negotiations are ongoing... when Syriza first came to power, the idea of GDP-linked debt was raised. This seems to have fallen off the table, but it might provide a "face saving" way out: the IMF's knack for optimistic projections could be helpful in making the value to the creditors appear initially large. Since they would have some equity-like characteristics, replacing the debt with GDP-linked bonds would have some passing similarity to what normally occurs in a corporate bankruptcy, where creditors receive equity stakes (and perhaps this would help make a "fairness" argument). And it actually might work: if the chances of future austerity and/or a euro exit were substantially reduced, Greece should have a chance at some rapid "bounce back" growth. I don't know anything about Greek politics, but I would think that, in the long-run, a government led by an "outsider" party like Syriza might have a better shot at implementing structural reforms like better tax collection.
See also: a good "tick-toc" on the negotiations from the Times' Landon Thomas on the breakdown of negotiations last week; Ambrose Evans-Pritchard; Ashoka Mody is very harsh on the creditors and the IMF, Daniel Gros is a bit more sympathetic.