HAVANA – The ouster of Cuba's two most prominent younger leaders leaves more doubt than ever about who will guide the country once the Castro brothers and their gray-haired revolutionary contemporaries are gone. President Raul Castro is 77. His hand-picked No. 2, Jose Ramon Machado Ventura, is a year his senior. And there are no obvious next-generation successors in the ranks of mostly obscure communist party officials, military officers and bureaucrats who were suddenly promoted this week in Cuba's largest leadership shake-up in decades. "This is the old guard, most of them are very traditional hard-liners," said Uva de Aragon,...