Preheat oven to 475 degrees. On a rimmed baking sheet, toss squash and onion with oil and arrange in an even layer; season with salt and pepper. Add sausages to sheet. Roast until vegetables are just tender, 15 to 18 minutes. Heat broiler. Sprinkle Asiago and sage over vegetables and broil until cheese is browned and bubbling and sausages are cooked through, 3 minutes. Sprinkle with cherries to serve.