Norman does not die. It is revealed in the manga that Norman is alive and plays a huge role in the human resistance against demons. He was handed over to a scientist, named Peter, by Mama Isabella to aid him in his research.

Did Norman actually die?

Norman is, however, forced to be shipped before his 12th birthday, and he sacrifices himself and accepts his fate of inevitable death to let his family escape.

Why wasnt Norman killed promised Neverland?

Norman reveals that after Isabella had taken him to the front gate, he was instead passed to Lambda rather than be killed like the others. This is a lab where demons drugged and experimented on children in order to mass produce better quality meat.