Heat oil in large skillet over medium heat. Decase and add sausage, breaking up into small pieces with wooden spoon. Cook until browned and fully cooked through, approx. 8 – 10 minutes. Place cooked sausage on paper towel lined sheet and let cool.
In a large pot, melt butter. Add onion and cook until soft, about 10 minutes. Add mushrooms and cook until soft, approx. 8 minutes. Stir in wild rice. Add broth, sage, and bay leaves. Increase heat to high; bring to a boil. Reduce heat to low and cover, cooking for 25 minutes.
In same pot, stir in basmati rice, cover and continue to cook until both rices are tender; approx 20 minutes. Remove from heat, remove bay leaves, and stir in cooked sausage and parsley. Add salt and pepper to taste.
Preheat oven to 350° F. Transfer rice mixture to butter casserole dish and bake until heated through and browned; approx. 20 minutes.