Alma 45:18

and when Alma had done this, he departed out of the land of Zarahemla, as if to go into the land of Melek.—And it came to pass that he was never heard of more; as to his death or his burial, we know not of.

When Alma had done this, he left the land of Zarahemla as if to go to the land of Melek. He was never heard of again. We do not know about his death or his burial.

After this, Alma left the land of Zarahemla, heading as if toward the land of Melek. He was never seen or heard from again. No one knows what happened to him or where he was buried.