Veniamin Fleischman (Rothschild's Violin, finished by Shostakovitch); Jehan Alain, killed a dozen Germans before they killed him, he had some of his music with him when he died; Dick Kattenberg, Dutch composer who was killed in the camps along with Leo Smit, every time I have read about Kattenberg, there are superlatives about what music he left, hopefully some will be played. And Hugo Distler committed suicide as a result of being conscripted into the German army, though that's not a battle casualty, if you have heard any of his music you know more and even better would have come from him, fragile soul that he was.