They're all alive. They surrendered. There weren't 13. Instead, there were 82. This was customary wartime propaganda and Zelensky's government created and perpetuated the lie, even going so far as to discuss the honors and funeral plans for the "13."
Now, I know, I know, lying through propaganda is okay when it's "our side." The truth being a minor casualty when such fibs are told. It goes without saying that if you point out these lies, you are, in fact, a Russian "asset," and an opponent of democracy.