Line bottom and sides of 9 x 5-inch loaf pan with plastic wrap; set aside. Drain cherries, reserving syrup. If necessary, add enough cold water to reserved syrup to measure 1/2 cup. Cut cherries into quarters. Completely dissolve gelatin in boiling water. Add measured syrup. Stir in yogurt until well blended. Chill until mixture is thickened but not set, about 45 minutes to 1 hour, stirring occasionally. Gently stir in cherries and whipped topping. Pour into prepared pan; cover. Freeze until firm, about 6 hours or overnight. Remove pan from freezer about 15 minutes before serving. Let stand at room temperature to soften slightly. Remove plastic wrap. Cut into slices. Makes 12 servings. NOTE: Cover and store leftover terrine in freezer.