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.
One thing you have to understand is that it becomes difficult for you buy and sell bitcoin if the government bans it and all the exchanges in India will close down,so there is a problem if they ban bitcoin,if they ban it they will implement money laundering case against the users.