I think officials claiming 'Grexit' are trying to fight for a better hand for future negotiations. If you look at where Greece is located in the contexts of various maps like EU and NATO, it has been one of the few stable countries surrounded by much less stable countries in the Balkans and border to the east. It would be a huge mistake for western powers to allow Greece to fall under the sphere of influence of eastern powers, or to entirely destabilize. That's just asking to bring trouble to what is literally the doorstep to the west.
Also I think the EU is a strange structure. Tying your currency to bigger powers with more resources than yourself is a mistake if there is not also a political union, specifically because of situations like this. Germany and Greece play in different leagues, and just like northern states in the US often end up feeding southern states money, the same will happen in the EU from richer to poorer states. What they get in return is influence, stability, a larger market, etc. If the EU members cannot accept this the union will ultimately fail. Of course, the EU does also need a means to influence policies of its member countries, but the method by which they have so far been trying to do it is at best ineffectual and at worst highly divisive, as evidenced by this turn of events. I don't really have the answer to this one though

They'll have to figure this out for the future.