Lightly grease a 3-quart rectangular baking dish; set aside. In a 4- to 5-quart Dutch oven cook bacon over medium heat until crisp. Remove bacon and drain on paper towels, reserving 1 tablespoon drippings in Dutch oven. Crumble bacon; set aside. Add onions, celery, and sweet pepper to the reserved drippings. Cook over medium heat about 5 minutes or just until vegetables are tender, stirring occasionally.
Add 4 1/2 cups broth and wine to Dutch oven; bring to boiling. Stir in barley. Return to boiling; reduce heat. Simmer, covered, for 25 minutes. Stir in squash. Simmer, covered, about 20 minutes more or until squash and barley are tender, stirring occasionally. Remove from heat. Stir in crumbled bacon, snipped sage, salt, and black pepper. Transfer mixture to the prepared baking dish.
Cover baking dish with foil. Chill for 2 to 24 hours.
To serve, preheat oven to 350 degrees F. If desired, drizzle squash mixture with 1/4 cup broth to moisten, stirring gently to combine. Re-cover with foil. Bake for 45 to 55 minutes or until heated through, stirring once. If desired, garnish with sage leaves.