Bitcoin is not actually deflationary. Its supply grows constantly until it eventually stabilises. The fact that Bitcoin prices have fallen a lot is more because lots of new people have discovered the project and decided they want some, but that effect will eventually peter out as Bitcoin becomes boring and everyone finalises their opinions of it.
Greece doesn't need fiat currency. What Greece needs is hard money – like the Euro (which is hard-ish, though not as hard as Bitcoin). This is because the Greek government is notoriously corrupt and the fact that they couldn't just print the pensions of their civil servants was one of the few things creating pressure to reform, and preventing outright pillaging of the savings of Greeks who do actually work in the private sector. Seeing Greece as one monolithic entity isn't right: there are different factions, not all of whom want the government to suddenly be able to spend whatever it wants. Hence the Greek people apparently voting for both keeping the Euro and not enacting any spending cutbacks, a contradictory position.
Ultimately Greece is going to get a lot poorer, no matter what. In many ways it's practically a third world country, one that was simply kept afloat by huge injections of foreign cash. But it never really stopped being third world in the way that it was run.
Bitcoin could, theoretically, benefit some Greek people now in the heat of the crisis because the Greek government wouldn't be able to impose capital controls on it. Thus preventing the outright theft of whatever little cash Greek's have left in the bank (sorry, I mean, solidarity tax/haircut/pick euphemism of choice). It is no magical cure for Greece's problems but it could tip the balance away from a government that discovered it was paying salaries and pensions for entirely non-existent departments, and towards people who are just trying to make a living.
