The obvious answer, although not I suspect the one you are looking for*, is that English would become extinct in the same way as thousands of other languages have become extinct over the ages: that is it would be replaced by another language. The new language might contain a single word derived from English in the same way that there are undoubtedly extinct languages whose only relic is a single borrowed word that has been adopted into some living language.

As Chris J said in the comments to the question, the quote from 1984 does not mean that people will be reduced to only being able to say one single word. That would make humans unable to think at any level above that of animals, which even the totalitarian tyranny of Ingsoc did not aspire to. The intention behind Newspeak in 1984 was "merely" to remove synonyms and antonyms. The link takes you to the Wikipedia article on Newspeak, which says:

This would, of course, not prevent heretical statements such as "Big Brother is ungood," but not only would this statement sound absurd in the ears of the politically orthodox, it would also be impossible to elaborate on or specify exactly what the statement means since all concepts and words that can be used to argue against Big Brother (i.e. liberty, rights, freedom, etc.) would be eradicated from the language. The statement would thus be meaningless.

For how the change to the restricted vocabulary of Newspeak was to be accomplished, I refer you to 1984 itself. It was described as being done over decades by a mixture of propaganda, rewriting of history and previous literature, censorship, social pressure and - of course - terror.

I think you have been misled by Orwell's use of the word "every" in "Every concept that can ever be needed…". He meant it in the same sense as "each", not that all concepts would be melded into one word. To literally destroy human language would require raising babies in isolation from any human society, as has sometimes happened with "feral children" who were abandoned or lost as babies but survived among animals.

But to raise children in isolation would require those making the practical arrangements to bring this about to communicate among themselves. This would mean that more complex language survived somewhere, unless, as Nex Terren's comment suggested, those doing the raising were robots.

If the children were raised in isolation and denied interaction with other people during the language-forming phase of early childhood, they would grow up to be severely intellectually disabled. If, however, they were prevented from communicating with adults but not from each other, then I think that the innate human language ability would reassert itself in some form, not necessarily a spoken form. Consider how Nicaraguan Sign Language evolved.

*The edit to the question saying that answers should not be limited to the universe of the book 1984 was made while I was writing this answer.

The obvious answer, although not I suspect the one you are looking for*, is that English would become extinct in the same way as thousands of other languages have become extinct over the ages: that is it would be replaced by another language. The new language might contain a single word derived from English in the same way that there are undoubtedly extinct languages whose only relic is a single borrowed word that has been adopted into some living language.

As Chris J said in the comments to the question, the quote from 1984 does not mean that people will be reduced to only being able to say one single word. That would make humans unable to think at any level above that of animals, which even the totalitarian tyranny of Ingsoc did not aspire to. The intention behind Newspeak in 1984 was "merely" to remove synonyms and antonyms. The link takes you to the Wikipedia article on Newspeak, which says:

This would, of course, not prevent heretical statements such as "Big Brother is ungood," but not only would this statement sound absurd in the ears of the politically orthodox, it would also be impossible to elaborate on or specify exactly what the statement means since all concepts and words that can be used to argue against Big Brother (i.e. liberty, rights, freedom, etc.) would be eradicated from the language. The statement would thus be meaningless.

For how the change to the restricted vocabulary of Newspeak was to be accomplished, I refer you to 1984 itself. It was described as being done over decades by a mixture of propaganda, rewriting of history and previous literature, censorship, social pressure and - of course - terror.

I think you have been misled by Orwell's use of the word "every" in "Every concept that can ever be needed…". He meant it in the same sense as "each", i.e. that each of a limited set of concepts would have one word, not that all concepts would be melded into one word. To literally destroy human language would require raising babies in isolation from any human society, as has sometimes happened with "feral children" who were abandoned or lost as babies but survived among animals.

But to raise children in isolation would require those making the practical arrangements to bring this about to communicate among themselves. This would mean that more complex language survived somewhere, unless, as Nex Terren's comment suggested, those doing the raising were robots.

If the children were raised in isolation and denied interaction with other people during the language-forming phase of early childhood, they would grow up to be severely intellectually disabled. If, however, they were prevented from communicating with adults but not from each other, then I think that the innate human language ability would reassert itself in some form, not necessarily a spoken form. Consider how Nicaraguan Sign Language evolved.

*The edit to the question saying that answers should not be limited to the universe of the book 1984 was made while I was writing this answer.