That ASSUMES that Pakistan is able to detect a missile much before it strikes. It may be true for a ballistic missile but a cruise missile flies much lower than a ballistic missile and distance here are not massive. At mach 3, it will cover 450 KM in 7.5 minutes and you will detect it much later than a ballistic missile which you can detect when it goes up. So, very very likely you will only come to know about this missile has been launched when it actually hits your high value sites. This means at that point, you know what has hit you, a conventional or a nuclear weapon. So you cannot hide behind veil of strike on launch or launch on launch because you simply cannot detect launch and will not have enough time to react before missile hits.
Actually, even if you "go boom". You will not be able to do a finishing blow to India. Even after absorbing 100-300 nukes, India will survive, though it will be totally devastated. Remember, you have only 20-40 KT nukes.
At that point India will retaliate with its nuke and they have lot less to cover.
End result will be end of Pakistan and devastation but still continuation of India.
Now in 2019, India had declared a completion of military action after it unsuccessfully tried to hit places in KPK -- most likely deliberately. Funny thing is, for all the escalation, PAF deliberately launched glide bombs with fuses removed. It did not want to escalate at ALL. So 2019 was no measure of escalation capability of PAF or IA. BOTH were doing fake operation for popular demand in their countries. Had that Indian pilot not tried to pursue the escaping Pakistani aircraft, no missile exchange would have happened. It was a pure phoney conflict with no real fighting.