In general, it's a fallacy to look at the comic and declare that the most statistically probably outcome of an event is necessarily what is occurring, especially if doing so contradicts stuff that's explicitly stated elsewhere. Is it less likely for a Neutral character with good Will saves to take significant damage from Unholy Blight? Sure. But it's still possible, and in this case, it's what happened, because anything else would have cluttered the joke.
There was also no switch to Conjuration as a barred school, so much as I didn't decide what V's barred school was until later when I needed to eliminate teleportation as a possible plot-killer and forgot about the spiked tentacles. However, if you really need it to all fit together smoothly, just assume that anytime V is seen casting a Conjuration spell in the early part of the strip, he/she is actually casting Shadow Conjuration and everyone around her/him is failing their saving throw.
EDIT: To be clear, it is entirely possible that at the time I drew strip #11, I thought of V as Good. I don't remember. I'm saying that the continuity of the narrative is that V has always been True Neutral, and nothing in strip #11 contradicts that.