The last thing we know about him is that the animorphs kidnap him and take him to the New valley to use in the blackmailing of Erek. I don't know what happens afterwards, but I assme they didn't kill the Human Chapman. His Yeerk probably died. I don't think it's mentioned that he could morph, but I guess that wasn't important to the plot.
Jake threatened to kill Chaman if Erek didn't do what he said. Now we know Erek disabled the pool ship's guns, which allowed the Bladeship to get away, so it's possible Jake made good on his threat and killed Chapman for it. But since it isn't mentioned, I really don't know.