St. Mary’s in Yonkers with the Hudson River behind: Photo courtesy of Austap Wolfgang Klymko “We’re betting on the pope. We can’t help as much as we would like to.”Officials in Yonkers rarely invoke high ecclesiastical authority. But it’s also not often that a church like St. Mary’s, the city’s oldest church, faces the threat of extinction. It was Charlie Hensley, chair of the city’s Landmark Preservation Board, who said he was putting his money…