People will argue with me about this, but I’m going to say yes it is important. Knowing at least a little Hindi will set you apart from all the other foreigners. Just knowing please, thank you, hello, goodbye, etc really goes a long way to showing interest and respect.
And, in my experience here, the people I was most drawn to knew very little English.
Yes, you can get by without knowing anything. Most educated people will speak English, but you have to remember that their education is a result of privilege. Privilege insulates you from the harsh realities of the world and can even breed entitlement. In my experience people who feel a strong sense of their own entitlement are not only ignorant of the world but down right dull.
To meet all the coolest people, learn some Hindi.