The death of Mara in February 1959 unsettled Bell and he experienced a heart attack later that month. He converted to Catholicism that summer because of the lifelong urging of his wife, Mara's death, and his enduring friendship with Rooney, a practicing Catholic. Bell was advised by his doctor to avoid going to football games, to which he quipped, "I'd rather die watching football than in my bed with my boots off." Bell and his children attended an Eagles game on October 11 at Franklin Field against the Steelers (both his old teams). The Eagles held complimentary box seats for him and guests to watch the game, but he preferred to buy his own tickets and sit with the other fans. Sitting behind the end zone during the fourth quarter of the game, he suffered a fatal heart attack and died later that day at the nearby university hospital. League Treasurer Austin Gunsel was named interim NFL commissioner for the rest of the season.
Bell was criticized as being too strict with his refusal to let sold-out games to be televised locally. Nevertheless, his balancing of television broadcasts against protecting game attendance made the NFL the "healthiest professional sport in America", and he was the "leading protagonist in pro football's evolution into America's major sport." He had understood that the league needed a cooperative television contract with revenue-sharing, but he failed to overcome the obstacles to achieve it. He was portrayed by sportswriters as ensuring the owners treated the players fairly, and his decision to recognize the NFLPA in the face of adversity from owners was a "master stroke" in thwarting Congressional intervention. After he initiated terms for a pension plan with the players in 1959, little progress was made with the NFLPA, however, the first players' pension plan-the Bert Bell National Football League Retirement Plan, was approved in 1962.