It will probably take 2-5 minutes for a missile to reach another country.... answer to ur question yes pak will be left to respond... Coz one missile wont finish off whole pak will it? Plus pakistan have missiles in different parts of the country so if the indian missile strike islamabad than we can also gift india 2-3 missile either from sindh or somewhere else.....
Granted Pakistan will left with a response which i still believe that it will not. Strike Islamabad and firing missiles from sindh, if you don't mind can i ask what is your age ?