User blog comment:Chaos11394/Where Do the Demons Go?/@comment-101.162.163.153-20140111061414/@comment-88.193.27.90-20141202184445

It would kinda make sense, atleast to me that the demon smoke get's purified back into a pure soul and go to heaven where all soul's were supposed to go all along before Lusifer created demons and hell. And its dumb to say that demons dont have a soul when the black smoke actually is their soul isnt it, why else would the demon cure thing work, that Sam by the way didnt complete properly when he cured Dean. So i think killing the demons is just a rough way of curing their soul's.