They can't wait until summer. The interesting thing is that there really is no government in charge. No one is willing to make this call and take the blame for the result. It's like watching a train wreck in slow motion.
Socialist governments aren't known for their economic savviness.
I suspect that, if the drachma is revived, the Greeks will run the presses to pay for anything they can buy with drachma, default on obligations that cannot be paid in drachma, and hope for a flood of tourists with lots of (relatively) hard euros in their wallets.
If that scenario develops, of course it will be hard to pay for imports (about 40 billion euros per year) but a drastically devalued drachma is going to make their manufactured and agricultural goods attractively priced relative to the euro. I wouldn't be surprised to see some continued upsurge in their exports (currently about 20 billion euros per year) if the drachma is revived.