User blog comment:EmpyreanSmoke/Supernatural Q&A/@comment-4632123-20150813211437/@comment-24834479-20150819000705

This is very interesting, and something the writers talk about a lot. While there is no definite answer to what happens to demons after death, there are some discussions around the writing room. The first idea is that the twisted soul is actually destroyed; gone forever. The second idea is that there is another afterlife which imprisons their souls after they are killed. The last idea, which you just said, is that like ghosts, their bones tie them to earth, and by burning them/stabbing them with a angel/demon blade, you break the connection, and lock them in hell forever. The first two are the most accurate theroies as of now, though.