I'll admit, I didn't particularly care for either Zahariel or Nemiel. Their back-stories weren't particularly interesting to me; their relationship never seemed to go beyond seemingly forced familial love and competitiveness; neither struck me as a full-fledged, distinct character. Zahariel just seemed to serve as a point-of-view character in some frustratingly vague situations. Nemiel just seemed to serve as a vehicle for some pretty frustrating assumptions about the Lion.
That having been said, I didn't care for the way Nemiel was done in. At the time, it felt like an instance of author's fiat. Was it? I don't know. On the one hand, I wouldn't be terribly shocked if the creative team decided this particular plot line wasn't going anywhere anytime soon, wasn't generating enough interest, and/or wasn't particularly fun to write. On the other, I hesitate to accept that Thorpe would end someone else's work in so blunt a manner.
I've come to think that Nemiel's death was indeed meant to end that particular plot line (which I'm guessing was meant to culminate with a confrontation between the chaplain and Zahariel), but was also meant to give birth to different angles. The problem is, I can't really think what those could be, other than some tired, oft-trod stuff. Nemiel's death could, for instance, fuel moral relativism argument (of the rather poor sort that we saw raised between Curze and Vulkan) between Zahariel and [insert Loyalist Dark Angel] when the Battle of Caliban happens: "You're no better!" type of stuff. At the very least, it strikes me as an attempt to get the Lion back into "mysterious", "might he be a bad guy?", and "could the complaints against him have been justified?" territory, since him being a taciturn, conflicted, but nonetheless noble and well-meaning wasn't (for some reason) enough.
Two things frustrate me about this situation:
1. I feel a great opportunity was missed. In noble Corswain and uncompromising Nemiel, the writing team had two characters who (assuming they survived the Heresy) could serve as a perfect microcosm of the conflict the Dark Angels went through when knowledge of the Fallen surfaced and the Inner Circle came to prominence. That would have been a delicious clash; both characters feeling they are fighting for the soul of their Legion, with one fanatically driven to destroy the lost cousin he thinks personifies Caliban's betrayal and the other trying to hold on to the tenets and ideals that once defined his brethren.
2. The story this happened in, The Lion, was just really hit-and-miss for me. This is the same tale in which Thorpe introduced the most obvious deus ex machine device* in a while (literally, the solution to the conundrum of Thramas Crusade); and rather ham-fistedly had a decidedly loyalist primarch release the right-hand man of an avowed traitor primarch. In that sense, it was a case of bad news after bad news after bad news.
* Tuchulcha may very well not have been someone else's baby. I don't know. I sincerely hope it wasn't Thorpe's in the same way that I wouldn't wish it on any other author. At best, it's a questionable sequel to Fallen Angels in the sense that the Lion is going after yet another secret/forgotten relic that can end the war. Really, it just serves as an excuse to yet again not have to try to convey some of the genius a primarch brings to the battlefield. That is, why try to solve the Thramas Crusade conundrum with strategy when you can introduce warp tech that allows you to perfectly ambush your opponents?