You talk as if India is as strong as America and Pakistan is as weak as Maldives... There cannot be any guarantee given that we will be able to neutralize the launch and eliminate entire nuclear arsenal and Pakistan won't be able to hit even with a single nuclear warhead....India's policy of not using nuclear weapons against Pakistan is based on the fact that Pakistan lacks the capability to launch a nuclear strike on India. It’s a wise policy because if Pakistan attempts to use nuclear weapons against India, India would not only neutralize the launch but also eliminate all of Pakistan's nuclear installations and, like in 1971, invade Pakistan, withdrawing only once its objectives are achieved.
However it will be stupid to think that after nuking India Pakistan will get away with it due to your imaginary Indian policy of not nuking Pakistan...