They can already do this, and they don't thanks to

1) Their no-first-use policy

2) Pakistan already having nuclear weapons

US money that funded Osama, current money that ends up funding Pak Army/ISI seems to be a lot greater factors in destabilization of Pakistan than anything India has ever done.

For example I never understood USA providing F16s to Pakistan. It is nothing but USA's attempts to escalate the tensions.

And India needs ICBM for that ? If India wants to wipe out Pakistan off the map it is perhaps the easiest things to do than developing some nuke technology.