[swatkat]

You don't need a bank account to exchange demonetized currency notes.

[Manishearth]

You need ID, though. See https://news.ycombinator.com/item?id=12947147

You need a bank account for this process to be convenient and easy. Without it you have to exchange in bits and pieces.

[danparsonson]

No, but having a bank account and therefore a payment card a) gives you another means of paying for things besides cash, and b) likely means that you don't have your life savings in the form of now-invalid currency.