Seconded. I don't know anything about modding but at least he doesn't need voice acting. As it stands, in the light side path there is an overabundance of Mira/Hanharr content on Malachor V, so I'm wary about adding more. There is no need to add a death scene if Mira makes her way to the Trayus academy on her own, since it is implied that she leaves Hanharr to die of his wounds. In the other case, where Hanharr guides Mira to the academy, he does so because he hopes to see Kreia destroy Mira, so he could possibly be watching in the shadows as the companions ambush Kreia. When they're all beaten by Kreia, maybe he moves in for the kill (Mira) but Kreia kills him because she needs the companions alive to test the Exile.
For the dark side path, your idea is pretty good. Since the dark side path can have Disciple vs. Atton or Visas vs. Handmaiden, I think it is more thematic for Hanharr to betray you and attack in a moment of weakness, and you have to put him down. This fits because he hates whoever holds the bond of his life debt. Maybe he goes crazy due to the dark side energies of the planet so he forgets all about being "broken" to you and goes for it.