And those stuck with Drachma cant buy bitcoin since noone will sell BTC for a useless currency....
The Drachma will be having some value, as Greece exports billions of USD worth of agricultural produce, medicines and metals every year. But the initial exchange rates will be highly unstable, and it will be a very tough task for the Greek central bank to stabilize the exchange rates (that is, if they have the resources to do so).
Yes, most likely it will be inflated initially. The government will have to issue new money to pay debts, government employees (a large percent) and so on. Though, this should be limited by the EU in some way as well. However, if they don't change something in their economy eventually, who know where their inflation will stop.