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.
Add sausage to gumbo; cook 30 minutes. Stir in green onions; cook for 30 more minutes. Remove and discard bay leaves.
Remove gumbo from heat. Sprinkle with filé powder, if desired. Serve over hot cooked rice. Garnish with chopped green onions, if desired.