Actually I believe in what little lore we got in D1 (and maybe that Book thing people keep mentioning), it's implied pretty heavily that the traveller left BEFORE the darkness got there. The ghost says in D1 that before us, 'there had never been a guardian, and there had never been a ghost'. Somewhere I recall reading these blurbs that either heavily implied or outright stated that the traveller, until us, would just uplift each society it came across, then leave. Maybe it would give them some special piece of technology, but that's all. I think it tried to fight a few times, but not the way it did with us. With the Fallen, it stayed only long enough to usher in their own personal 'Golden Age', then left them, but when the darkness came (and the traveller was long gone) that 'age' ended, and so they sought out the traveller again to aide them. Hence why they're so pissed off at us for 'stealing' it. I will admit, though - that idea of our dying giving some kind of sustenance to the traveler is interesting - I don't think it's what they'll go for, but it's interesting, for sure~