Cook sausage in a Dutch oven over medium heat, stirring constantly, 5 minutes or until browned. Drain on paper towels, reserving drippings in Dutch oven. Set sausage aside.
Cook chicken in reserved drippings in Dutch oven over medium heat 5 minutes or until browned. Remove to paper towels, reserving drippings in Dutch oven. Set chicken aside.
Add enough oil to drippings in Dutch oven to measure 1/2 cup. Add flour, and cook over medium heat, stirring constantly, 20 to 25 minutes, or until roux is chocolate colored.
Stir in onion, bell pepper, and celery; cook, stirring often, 8 minutes or until tender. Gradually add 2 quarts hot water, and bring mixture to a boil; add chicken, garlic, and next 5 ingredients. Reduce heat to low, and simmer, stirring occasionally, 1 hour. Remove chicken; let cool.
Add sausage to gumbo; cook 30 minutes. Stir in green onions; cook for 30 more minutes.
Bone chicken, and cut meat into strips; return chicken to gumbo, and simmer 5 minutes. Remove and discard bay leaves.
Remove gumbo from heat. Sprinkle with filé powder, if desired. Serve over hot cooked rice. Garnish, if desired.