Disappearing nevi are called halo nevi. Many times moles will "disappear" without cause. The white or hypopigmented areas that are left behind will repigment with time.
Outside of cosmetic make-up, there really aren't medical treatments to repigment the skin. Make sure you use sun protection as these areas are more susceptible to sunburn. I might add that you should see a dermatologist to ensure that none of your moles are worrisome.