This is how Dean defeats Lucifer: he starts hearing or remembering a particular song, either "All Along The Watchtower" or "Carry On My Wayward Son" (because both are in sync with being religiously symbolic) which he starts miraculously playing on a guitar or a piano and that somehow gives him the strength/courage/clue/whatever to fight Lucifer. Through the ~coordinates~ and ~notes~ he finds there or with inside of himself, or whatever, and it will destroy Lucifer somehow without him being something superpowered or having to be an angel condom. God will make a special appearance too, possibly in the guise of Tricia Helfer, James Callis, Queen Latifah or Lady Gaga.
AND THEN ALL WILL BE WELL IN THE WORLD. CASTIEL WILL REGAIN HIS FAITH IN GOD, HE AND DEAN WILL HAVE LOTS AND LOTS OF HOT MAKEUP!SEX AND THEN THEY ALL GO TO DISNEYLAND WITH GABRIEL AND LITTLE JESSE TAGGING ALONG, WHERE THERE WILL BE CAKE AND ICE CREAM AND UNICORNS OVER SPARKLING RAINBOWS. :D
This is what my version of canon looks like. Your reality is irrelevant, kthx.