In the name of Allah
First and foremost the event you mentioned is incorrect, the truth is that eight Qadiyanis were killed and less than 20 were injured. This has got nothing to do with the earthquake which occurred in Pakistan. This statement was also made by a Qadiyani. It was the will of Allah the Creator that the earthquake took place when it did and the two events are not related.
It is mere coincidence that the earthquake happened when it did. The earthquake killed people from all religions including true sincere Muslims, Qadiyanis (or Ahmadis), Hindus, Shia's, men, women and children from all walks of life and has effected countless others all around the world. The reason behind the earthquake is not that what you have mentioned because the true Muslims are the enemies of many people and religions of the entire planet. I am very sure that many religions make such supplications against the true Muslims who believe in the finality of Rasul Muhammad but we see that true Islam is still flourishing by the will of Allah, dispite the efforts of the those outside the fold of Islam.
Allah himself says in the Quran, Fain would they extinguish Allah's light with their mouths, but Allah will not allow but that His light should be perfected, even though the Unbelievers may detest (it). 9.32
In another verse Allah says: Their intention is to extinguish Allah's Light (by blowing) with their mouths: But Allah will complete (the revelation of) His Light, even though the Unbelievers may detest (it). (61.8)
As mentioned in the Quranic verse above Allah will not allow but that His light should be perfected, if the non-believers make Dua against the genuine Muslims and authentic Islam in order to finish them, like you have mentioned, then this will not transpire due to the verse above. It is possible that it may transpire upon the few individuals involved in such crimes if they were unjust and evil and acted outside the Shariah (Islamic scared law) but that is in the power of Allah.
Such natural occurrences are not always related to human activities.
It is narrated from Al-Mughira bin Shu`ba: "The sun (solar) eclipsed in the lifetime of Rasulullah on the day when (his son) Ibrahim died. So the people said that the sun had eclipsed because of the death of Ibrahim.
Rasulullah said, "The sun and the moon do not eclipse because of the death or life (i.e. birth) of someone. When you see the eclipse, pray and supplicate to Allah." (Sahih Bukhari 2.153)
No one knows what the will and wisdom of Allah is behind such tragic events, and it is not always easy for the human mind to try and comprehend this wisdom. Duas of disbeliveers can be accepted by Allah, for he is all powerful. But in this case it was not due to this, as the earthquake killed virtually thousands upon thousands of people from every religion. But on the day of resurrection it will be the believers who will be separated and entered into paradise.
If anyone is to question their Iman upon such events then there is possibility that such person could be the case of bringing about such calamities.
May Allah save guard the Iman of your friend and of all the true sincere Muslims around the world. Ameen
And Allah knows best
9 October 2005