Costello retired in 1950 in order to join a seminary and become a priest. Father Costello helped to create a hockey team called the Flying Fathers in 1962, which raises money for charities by touring North America. The team is still around today.
In 2002 at a Flying Fathers game in Kincardine, ON, Costello was struck in the head by a puck, falling back and hitting his head on the ice. He was admitted to the hospital the next day, where he slipped into a coma and died a week later on December 10. (Link)