The phrase "are extant" refers to something that still exists or is currently in existence. Antonyms for this phrase would be words that describe something that no longer exists or has ceased to exist. Words like extinct, vanished, disappeared, or destroyed can be used as antonyms for "are extant". An object, animal, or plant that is extinct is no longer present in the world, while something that has vanished has disappeared without a trace. Similarly, something that has been destroyed is no longer in existence. Using antonyms for "are extant" can help to provide a more precise description of the state of something.