Preheat the oven to 450°.
On a baking sheet, toss the peaches and lemon juice. Place the sausages and onion alongside, drizzle with wine and top with thyme. Drizzle with the oil; season with salt and pepper. Roast until the sausages are cooked through and the onions and peaches soften and char in spots, about 25 minutes. Douse with the vinegar. Arrange on plates; top with the mint.