What to do after Pakistan uses nuke? would be a pointless excerise. There is nothing worthwhile to nuke in Pakistan.
We dont want to capture Pakistan, even they invite us to. Pakistan did a huge favour to India in 1947. They took all the nutcases out of India and left the good people back.
When India talks about "un-acceptable damage to them", we dont even know who "they" are. Pakistanis population/people, politicans, army?
If Pakistan is happy to show the world that it is irrational, then india needs to show to that world that it will become ir-rational if Pakistan fires nukes. Everything that is considered human by the world should be throw out of the window.
India has a bizzare problem of worrying about nukes from a country, whom we dont even want to touch with a long barge pole!