Why we will not do anything? - You think there is any alternative? - We cant let Pakistan become a desert -
Pakistan will do, what it can affoard to do (a big hue and cry on international forums, acts of terrorism here and there), but stop short of mass committing suicide.
Because Intelligent and self centered Pakistanis at Pakistan's helm, realize that people can live in a dessert (ask your Saudi cousins) but they cant live in a nuclear wasteland.