Preheat the oven to 375 degrees F and butter a 3-quart baking dish. Melt 2 tablespoons butter in a large skillet over medium heat. Add the sausage and bacon and cook, breaking up the meat with a wooden spoon, until browned and cooked through, 6 to 8 minutes. Remove with a slotted spoon and transfer to a plate.
Melt the remaining 6 tablespoons butter in the skillet, then add the onion, celery, apples, sage, thyme, 1 teaspoon salt and a few grinds of pepper. Cook, stirring, until the vegetables are tender, about 5 minutes. Add the cider. Bring to a boil, scraping up any browned bits, and cook until reduced by half, about 5 minutes. Add the broth and return to a boil, then remove from the heat.
Whisk the eggs and parsley in a large bowl. Add the bread, sausage and vegetable-broth mixture, cherries, and parsley, and stir until combined. Transfer to the prepared baking dish; sprinkle with the walnuts and drizzle with butter.
Cover the dish with foil and bake 30 minutes, then uncover and bake until golden, about 30 more minutes.