I think it comes down to a preferred style of play. This encounter is either no win from one point of view or always win from another.
How is it ever a win?
The NPC dies. Loss.
The PC gets knocked unconscious. Loss.
The PC dies. Loss.
THe NPC dies. Oh no wait, that cannot happen. Even when the PCs kill him, he is either not dead, or saved, or replaced with a clone.
It seems like lose lose to me. It seems like heavy handed DM (actually designer) manipulation.
And yes, I get the whole "the villagers are saved". Woo hoo! The PCs are heroes (or at least after the one PC wakes up, if he wakes up). It just seems like a hollow victory.
Ah, I see the confusion. The adventure accounted for the Death Saving Throw rules (p. 76 of Basic Rules), but didn't account for the Unconscious condition in Appendix A.
At this point, I'm more inclined to see this as an editing mistake due to the adventure being written while the rules were still in flux, rather than the writer's changing the rules to baby the PCs.
Yeah, I've heard that there are quite a few "editing mistakes".
Yes, it is a change. If a creature is at zero hp and unconscious, then any attack that hits the creature is a critical hit if the attacker is within 5 feet of the creature. Therefore, if Cyanwrath hits you to zero and you drop, then the module specifically states he gives you another blow while you are done. But instead of using the rules of the game, in this particular instance it is changed and the hit is not considered a crit.
The question is, where are the other PCs at this point? Are the PCs on the parapets? Are they on the ground? How far away is the duel? People have posted different ranges for the duel.
Even if the other PCs can get close after the fight, what happens if there is no PC with the Spare the Dying, hence, no longer range stabilization? Or has a Heal potion? Or misses the DC 10 Medicine check to stabilize?
Playing the rules as written in the PHB, or even as per the module, could fairly easily result in a dead PC depending on the situation and dice rolls.
Yes, the DM can hand wave that away. But he shouldn't have to.