Dark leafy greens such as kales, mustards and chards have a tendency to wilt as they sit in the refrigerator, especially if they are not stored correctly. (Click here to see the method I prefer for storing greens.)
However, if wilting does occur, not all hope is lost. Revivifying is possible by soaking the greens in cold water for several minutes. They won't be as good as new, but you should notice a definite perking up. (Before photo above, after photo below.)
Some dishes that I've recently made which I've added kale to include chicken soup, macaroni and cheese, an omelet and a winter quinoa salad (with red cabbage, diced sweet potato and walnuts).