The aged Mormon was killed by the Lamanites, and verse 5 adds the detail that he was “slain in battle.” Obviously this was not a pitched battle, so Mormon was either resisting capture or, more sinisterly, had been pitted in a mock battle as a form of human sacrifice. Such mock battles were a form of human sacrifice known from later Aztec practices.
H. Donl Peterson, LDS author, suggests that Moroni was thereafter completely solitary. True, Moroni states, “I even remain alone,” but I read this statement as hyperbole. He was without kin or country, but surely some former Nephites would have assisted Moroni during these years.