Toss potatoes, oil, salt and pepper in a large bowl until coated. Spread out in a large heavy roasting pan. Roast 10 minutes. While potatoes roast, stir sausage, apples mustard, maple syrup and vinegar together in the bowl.
Reduce oven temperature to 375°F. Remove roasting pan from the oven. Scrape potatoes up from the pan with a spatula. Add sausage, apples and the mustard mixture to the potatoes and toss to combine. Return to the oven and bake, stirring once or twice until the potatoes and apples are tender and the glaze is caramelized, 45 to 50 minutes.