Currently, Soothing Darkness is nerfed to 15% hp when you Vanish in PVP combat as opposed to the tooltip, which reads 30%.
Now that Soothing Darkness no longer includes Shadow Dance and Vanish being nerfed to 1.5 sec, I think it would be fair to bring it back to a 30% heal after using Vanish. For a 2min CD, its healing is awful, especially when you consider there is almost always a heal reduction of some sort in PVP, whether it be dampening or mortal wounds.