The Ukrainian soldiers and border guards on Snake Island, who told the Moskva, "Russian warship, go fuck yourself," were captured. The Putin forces gave Ukraine no word about them and Ukraine believed they were dead. In fact, they were imprisoned, and tortured, but not killed.

One, Bohdan Hotskiy, was eventually swapped for a Russian prisoner of war, which is how we know how he was tortured. The rest remain prisoners, as far as I can tell from this article.