cptnspldng - I am a bit of a conspiracy theorist here. I don't believe Justin died as it never happened on screen. In fact - Harry so rarely goes into detail about that fight (remembering the ENTIRE SERIES is him talking about his past, it is almost like he is avoiding it on purpose). I have a few reasons why that night is a blur - remember Harry didn't even recollect his encounter with the Walker HWWBH until he was dead and the Leanansidhe showed him. I am of the opinion that:
1. Harry (the narrator) recalls that at the time did not properly remember that fight (even if he thought he did - that's the tricky thing about memory).
2. Harry doesn't recall that fight as it truly was for more than mundane reasons (e.g. PTSD, poor memory recording abilities etc.) but because of interference (perhaps by himself, a time-traveler, some other monster/being or perhaps Justin himself). Never forget that while the binding on his body was one Harry himself had figured out, Justin was getting in his head even then.
Mr Death is correct in that the fight is in two parts (mostly because of inconsistency on JB's part). Part 1 is when he comes home from school and find Elaine being weird on the couch and Justin tries to convince him willingly into the fold, they fight and he uses the force of Justin's spell to smash him out a window and escape. Justin then sends the Walker to kill him (though it is implied and Harry muses that perhaps it was the Walker running the show) and he defeats the Walker - with a mixture of magic fire and gas explosion (which even Dresden later realises should not have worked - especially when you take into account this thing is supposed to be Uriel-level). Harry then goes back angry and duels Justin and is subdued by Elaine's binding. Justin then attempts to perform some strange ritual involving Harry consuming human blood for an unknown purpose, Harry breaks free and then...we only know that Harry uses fire to burn the house down. We have no other information. We never even had a body of either Elaine or Justin. Harry presumes them both dead for many years until Grave Peril where he has a dream where he realises Elaine might be alive. Then she shows up in the next book, a year-ish later. We only have Harry's word that Justin died (which was highly doubted at the time). Justin is Dead in Harry's mind because he wants it that way. Not because it is. See that whole passage about eye witness accounts in the series/remember Harry was just as sure Elaine was dead.
But I am of the opinion that considering how much Jim has said he is dead, he probably isn't. Jim wants to throw us off the scent. Not to mention Jim has said Death is a squishy line in the Dresdenverse. More like a threshold, you can cross and come back. Few do it, but it can be done. Not to mention, we know from the series that once you cross that threshold, you don't just stop existing. You go into the varying levels of the afterlife, beginning at being a spirit/ghost and moving on into the varying Heaven's and Hell's and all the inbetweens. Also Mab has said Death is not black but grey, it is a spectrum not a line. Which makes a lot of sense really.
So even if Justin is dead or has died - that is not to say he has stopped existing or is not involved in events behind the scenes. He may have not died, or he may have resurrected himself, or perhaps he works as a ghost or somesuch. But believe me, he isn't out for the count. He had a plan.
