For fifteen hundred years the English language had shown itself to be impervious to threats.

The Beowulf poet spoke Old English. Chaucer spoke Middle English. Shakespeare spoke Early Modern English. Tennyson and Wolfe and Woolf spoke Later Modern English.

Even if you make the unwarranted assumption that the quality of English-language literature has declined since Beowulf or Shakespeare or Virginia Woolf, that would be a defect of individual talent, not of the English language.

English would be truly threatened only if people no longer find it advantageous to use it. That's what happened, for example, to Cornish and Manx and any number of Third-World languages.

We may be irritated - justifiably - by sloppy and ignorant and intenionally deceptive usages, but if they don't sink out of sight on their own (as some do), they become fully assimilated and less noticeable to later generations - who then rail about their own pet peeves.

My prophecy: despite everything, some enduring masterpieces will be written in English in the 21st Century. And the 22nd...

They may not be to our taste, but Hardy, Hemingway, and Heller would not have been to Samuel Johnson's taste either.