All plants that are re-potted, unless they are at their prime (no wilting, etc.), will go through a period of stress. The roots have to acclimate. Because your plant was already wilted, I would think that you'll see some improvement within a week if you can do that misting. It should look good again within 2-4 wks. That just depends on how "happy" it is in its surroundings and how the care is.
One thing to keep in mind is that wilting is always a sign of stress, and with Peace Lilies, that is generally a sign of drought. Train your eyes to pick up on this since it will be constant with this plant. At the first sign of wilt, get that watering straight. Also, Peace Lilies are vigorous growers and form a dense root-ball pretty quickly. As they become root-bound, they need more frequent watering. For a four-year old plant, your plant is awfully small. Perhaps it has been root-bound for some time. You might know the answer to this. I am simply going by a single picture. Do you think your plant was root-bound when you re-potted?
