In a geopolitical scheme, Greece's location is very important, which is why these negotiations have been going for as long as they have. The Western/Northern Europeans know how the Greeks are and they have always known it, but, at the end of the day, they've always put up with them, because they had to in order to keep them on their side. The West, and more importantly the US, isn't going to waste so many resources poking into the Russians in so many locations only to let Greece go. Greece is a NATO member, Greece buys Western military equipment, etc. etc. etc. This is why Tsipras is on the phone with both Obama and Putin. Because he knows that if Merkel, Juncker et al. have the capacity to let them go, Obama doesn't, and so he uses Putin as leverage.
Realistically, there are two possible outcomes to this Greek drama. Either Tsipras finds the middle ground with the Europeans, because he is ultimately told to do so, as are the Europeans, or, in the case that he continues defying the will of the powerful, he's ousted and the Greeks accept whatever measures they're given. There's no doomsday scenario of an utter Greek collapse, not so long as the Russians and the Americans are beefing.