From here
"In 1947 there was a formal agreement between the trustees whereby the league was delegated the full authority ... making the Stanley Cup a competition for NHL teams," points out Gary Meagher, the NHL vice-president of public relations. He's right. You can check it in Total Hockey, 2nd Edition. Page 355. But wait...! The text goes on: "the agreement shall remain in force so long as the league continues to be the world's leading professional hockey league as determined by it's playing calibre, and in the event of dissolution or other termination of the National Hockey League, the Stanley Cup shall revert to the custody of the trustees."