Sauté mushrooms and onion in butter in a large skillet until tender. Stir in flour. Gradually add broth and milk, stirring until smooth. Cook over medium heat, stirring constantly, until thickened and bubbly. Remove from heat. Stir in chicken, rice, almonds, pimiento, salt, and pepper. Spoon into a lightly greased 2-quart casserole. Top with breadcrumbs. Pour butter over crumbs, and sprinkle with paprika. Bake at 350° for 20 minutes or until lightly browned.