Remove the rabbit from the pan and add the onions. Stir, season with salt and pepper and cook, stirring and scraping the bottom of the pan to release the browned cooking juices on the bottom of the pan as the onions begin to give up their liquid, until the onions are translucent and tender, 10 to 12 minutes. Return the rabbit and any juices it has given up to the pan, stir, then pour in all the wine and the water. Scrape up any remaining juices from the bottom of the pan. Add the herbs and the plums, pushing them down into the liquid,. Bring the liquid to boil, reduce the heat so the liquid is at a lively simmer and cook, covered,, until the rabbit is cooked through, about 35 minutes, turning the pieces at least twice during the cooking time.