leached? leached how? we talking the old timey remedy 'you're sick because you've got too much blood, throw some leaches on you!' or are we walking a highlander-esque 'there can be only one' and their powers were 'leached' by another.
either way i don't know of any. the former because so many people [witch and non-witch] were subjected to horrendous old time medicine it's hard to pick out a unique tale. the latter because real witchcraft isn't a Brothers Grimm fable. a witches 'power' [like to cast spells] isn't theirs to loose. it is a connection to the energy in the universe that can be manipulated/directed to achieve a goal [and since 'witch' is a title like 'Christian' or 'geek' anyone can do it, it's not the name but the person that matters.]