I really don't know how they legalize or i-legalize such thing as bitcoin because you are using it with your own internet and computer hardware maybe they just not supporting it before but every citizen of India can use it no matter what happens unless their government issue a criminal liabilities in using bitcoin.
any law regarding bitcoin (legal or illegal) is always about businesses. they can never force individuals to use or not use bitcoin.
so they place laws regarding:
- trading bitcoin in exchanges (exchanges are centralized place, like a business)
- accepting bitcoin (again a physical shop or an online one is known)
if they make it illegal, the exchanges close and the shops stop accepting bitcoin.
and if they make it legal exchanges open or continue and same with shops.
it's not like you use their own exchange which i never heard about, i mena india don't even have an exchange, and they can not certainly stop a foreign exchange like kraken, so even if it was illegal i would just sell abroad and receive on my bank account the money
but perhaps you mean that they would close your bank account if they find this kind of activity, which is another story, still you can use another foreign debit card and get the money anyway