Here I want to repeat the words of Zia ul haq to Rajiv gandhi...
" If you destroy us , there are several muslim countries in the world to continue the glory of Islam, but if we destroy you than that would be the end of hinduism on the face of earth" ( same message was conveyed to Israel through other sources)
It is sensational and scary statement when you hear it for the first time but I would like to think about this out loud. So, let's say Pakistan wipes out all of India and India wipes out all of Pakistan (plus other smaller countries in the subcontinent). First let us see what has the world lost...
a) Punjabis
b) Kashmiris
c) Sindhis
d) A big chunk of the Pathan population
e) A big chunk of the Baloch population
f) All of the Central North-Indian belt (delhi, Punjab, Haryana, UP, MP, Rajasthan, Himachal)
g) All of the north eastern population - again very different and rich culture
h) Western Coastal India - Maharashtra, Gujrat etc. again rich and different cultural heritage
i) Southern India - Completely different people - a race in itself - along with Sri Lanka
j) Easter Coastal India - Bengal, Orissa etc. again very different people along with Bangladesh
Now, we would have wiped out about half a billion Muslims and 1 billion Hindus and other people of faith.
World will continue as usual. In some ways it will be a better and safer place. It will now have 1.5 bn fewer people. Islam vs. Non-Islam will take a back seat atleast for few centuries after having witnesses an tragedy of such grand proportions. Povery will be almost eradicated. Global warming might take a reverse turn. Advantages of complete and sudden annihilation is that there will be no revenge wars to follow. World might have to deal with the radiations risk but other than that it will continue as usual.
As for the cultural heritage, it will become a subject of interest for people around the world to study. Some arts/knowledge/practices/thoughts will die but other survive. There is a chance that different dance forms might survive to some degree- like Bhangra, BharatNatyam etc. Languages might become extinct over time but atleast the recorded litreature available in Libraries abroad or on internet will survive. Certain unique values to the region like vegetranianism/yoga/non-violence might become extinct but will still survive as subjects of interest for people to study.
Hindu mythology in practiced and celebrated form will die but the records will still exist in libraries and in other media forms.
Regional Music will become extinct but a part of the popular existing music will be preserved.
But somehow to me it really doesn't matter if all the Hindus are gone from the world. I mean as long Humanity lives and prospers, it is fine, right?
All in all it is a good scenario for the humanity as long as the radiation risk can be managed.
I have more thoughts but I have to go...