User blog comment:Tommy,Klaus&Kol2012+/How to Kill a Levithan/@comment-3481504-20120225175225

An intriguing theory, but totally implausible. There's seemingly only one Phoenix, and Dean and Sam already used it's ashes in "Frontierland", therefore that item can't be used. Also, all of what you mentioned would only kill the human vessel, not the actual Leviathan.