Put oven rack in middle position and preheat oven to 350°F. Bring wine, vinegar, and sugar to a boil in a 3-quart heavy nonreactive saucepan over moderate heat, stirring until sugar is dissolved, then add figs and gently simmer, uncovered, 5 minutes. Pour figs with liquid into a 2-quart shallow glass or ceramic baking dish and sprinkle with walnuts. Bake, uncovered, until figs are softened and have absorbed about two thirds of liquid, about 30 minutes. Cool slightly, about 15 minutes. Serve warm figs with sauce and a dollop of mascarpone.