You have the option in Act 2, to tell Minthara that you have the artefact and she goes to see for her self. The rest of the game carries on and you are told to go to moonrise as normal. You get to moonrise and Minthara is being interrogated about not having the artefact and she has no idea where it is.
What on earth happened here, how can such a glaring plot hole have been missed?
Kethric doesn't seem like the understanding type...his initial reply would probably have been "What do you mean another True Soul is bringing it? It was your job. Why didn't you kill him and get it?" and proceeded right into the trial we see when we get there. I don't see them as much more caring or reasonable than the Gith patrol. So yeah, not that much of a plot hole or a mystery imo.
Nonsense. She was sentenced to death, and she acts like she has never seen the artifact before. Even if what you say has some plausibility to it there is no chance she would not have bought up the fact that the artifact was in the room at that time instead of acting like she has no idea where it is whilst her life is on the line because of that one specific object!
Furthermore, you have just uncovered another potential plot hole, why would she not have taken the artifact, after all it was her sole purpose? Instead she leaves it alone, and goes back to the general to report she doesn't have it, and does not know where it is?
For a game that boasts reactivity, they sure did leave it out for the meaty parts it appears.