Steve Wynn, who is to Las Vegas what Walt Disney was to theme parks, is losing his empire. Wynn’s Vegas theme resorts — the Mirage, Treasure Island, the luxury Bellagio, as well as other properties — are being acquired by MGM Grand Inc. for $4.4 billion in cash, it was announced yesterday. The move effectively ends the reign of Wynn, who since the ’80s has been considered the unofficial king of Las Vegas for his having revitalized the gambling mecca with his splashy brand of hotels and casinos. But Wynn’s new Mississippi casino, the Beau Rivage, is not performing as expected, while in Vegas Mirage customers are being lost to the Bellagio, which features a world-class art collection. As a result, Wynn’s Mirage Resorts Inc. has suffered on Wall Street. Wynn, 58, may start fresh with a new casino — or he may simply take his money (reportedly nearly $532 million) and retire, speculates The New York Times.