1. no longer in existence
Global climatic changes may have been responsible for the extinction of the dinosaurs.
They are in danger of extinction.
Some wild animals are on the verge of extinction.
Many fragile species are on the verge of extinction.
The Siberian tiger is on the verge of extinction.
Due to total russification in Belarus, the Belarusian language is at the brink of extinction.
There are many theories about the sudden extinction of the dinosaurs, but the real cause still remains anyone's guess.
Imogen of the Internet has created a seminal classification of thirty distinct varieties of chatspeak, some now facing linguistic extinction.
Many of the world's seven thousand or so languages are spoken only by handfuls of living people and are in danger of extinction.
Extinction is part of evolution.
3. die out
4. not now existing