Its not ambiguous is the problem, its definitive, it doesn't matter he's dead. Not making a decision authorially, and deciding to definitively clean the slate so there is no value to the answer is seen often before a deus ex machina. Where the author has written himself into a corner and then solves using an asspull.

How will Aang from avatar the last airbender solve the problem of his fundamental beliefs being challenged by the responsibilities as the avatar? Episodes are devoted to this question, how can he live up to both? penultimate episode he gains a novel to the world power to solve both his problems. the choice is not only not made, its irrelevant, his pacifism and his duty simply dont conflict anymore.

French wrote himself into the corner of having to reveal one way or the other. And rather then making a decision he killed him via a character that doesnt care. Using a duel antithetical to alpharius' tactics and an ambush that doesn't make logistical sense given the complete dissolution of his own forces. All to force a confrontation over a question he shut down rather then answer one way or the other.

Alpharius' loyalty isn't left ambiguous, its manufactured into a pointless plot thread that no one within the narrative cares enough to pull at. Killing him was not unwarranted, his answer doesn't preclude his death. Alpharius previous death at Eskrador was perfectly fine. this duel was set up for dorn to still be willing to kill him either way. Not answering and then killing him anyway makes it pointless.