It's possible you're thinking of a few things:
* The letter Z is used less frequently than other letters: It's true that "Z" is one of the less common letters in the English language, but it still has a vital role in many words.
* The letter Z has a different pronunciation in some words: The letter Z can be pronounced differently depending on the word, which might make it seem less familiar to some people.
* Some historical texts or dialects may have used different spelling conventions: Historically, there were variations in spelling, and some words might have used alternative letters or spellings. But this doesn't mean the letter Z has disappeared from the English language overall.
So, rest assured, the letter Z is alive and well in modern English!