Was unable to get 'The Mark of Defiance' or 'Vul'gath's End'.
I did this series slightly out of order as follows:
1) A Collection of Coils & another quest involving gathering the spears that is not listed here.
2) At the End of Your Rope - got quest but did not complete quest objectives
3) Tar Get of Opportunity - got and completed
4) Burn Them Down (completed objectives but did not turn in though I saw PC across from Vul'gath location)
5) At the End of Your Rope - This one should have been done sooner but it let me turn in the others and I was trying to figure out where the mobs where they were talking about (they'd been taken out by other players so there were none to be had for a bit). Once I figured out what I needed to do for 'At the End of Your Rope', I finally completed this, turned it in to the NPC at the cleft location and, as the NPC phased away, the 'The Mark of Defiance' banner appeared with quest marker. I didn't take that new quest because I was concerned about quest order so I went to the NPC in the new location (across from Vul'gath). I turned in 'Burn Them Down', the NPC started saying something about only one thing left to do and then the quest box went away and the NPC had nothing else for me.
I went back to the banner, thinking I'd pick that one up, but that one was gone too. I tried killing Vul'gath but no change. So, I'm stuck without being able to pick up 'The Mark of Defiance' or 'Vul'gath's End'. :\