First, the notion of language corruption is a political/socilogical one, not a linguistic one. Linguists do not assign value to language change.
Second, the situation you describe - at least, to the degree you describe it - is probably not a counter-example to what I'm saying. I don't know much about India, so I'm not talking about the specific case, but you hear about things like this a lot in the media, and 9 times out of 10 (at least) they are misinterpreted. A bilingual individual living in a non-bilingual community will only use one language at a time. When the community is bilingual as well, however, what people do is mix languages. That is not the same as creating a new hybrid language; rather, it is switching back and forth between two languages continually, sometimes within the same sentence (the technical term for this is code switching). The way you can tell code switching apart from a merged language is that the bilingual speakers are perfectly capable of understanding and using "pure" Hindi (or whatever their mother tongue is) when they go back to their families and other people who are not in full command of English.
Now, there is an interesting question here of what happens over several generations - once children grow up in a community where everyone mixes Hindi and English, do these children know they are listening to two languages or do they think they are hearing a hybrid? I don't know the answer to this, so I don't want to conjecture.
What I do know, however, is that in situations like the one you describe above, the most common result is either a stable bilingual community (if people in it have reason to use both languages), or, over time, the less useful language will mostly disappear, and the communities will become English speaking. The latter is certainly a possibility - but all I was saying above is that this will not happen on a global scale. There will be a lot fewer languages spoken in this world in 50 years than there are now, but there will still be many of them.
