User blog comment:EmpyreanSmoke/Supernatural Q&A/@comment-95.112.132.239-20150929104807/@comment-24834479-20150929234229

If Dean went back in time with the mark of Cain, and Cain was dead, then the darkness would not be released unless Dean cured the mark. I dead traveled back in time, he would still be immortal and live to the present.