Diego Marani has written a novel which has the last speaker of a language as a key character. Vostyach is a Finno-Ugric language, believed to have vanished, until a Russian linguist finds a last speaker who has grown up in the gulag. Unfortunately, she reveals her discovery to an unscrupulous Finnish linguist whose cherished hypotheses about the linguistic history of Europe are threatened by this new data.
How far he is prepared to go to defend his theories, and what happens to these various characters, you can find out by reading the novel (no spoilers!) – but I will say that the last of the Vostyachs himself ends up not too badly and his language is being heard by many people (at least in some form) by the close of the book.
Marani does not really use linguistics a great deal in this novel – there is some rather dodgy phonetics in there, and he doesn't go into any detail about either historical linguistics or language endangerment. It isn't great literature either (I read it on an international flight, and that seemed about right) but it is all highly entertaining.