OK, so I know the plot is set up so you are not supposed to kill Rentar-Ihrno. I already won in the traditional fashion.
Seeing as Avernum 4 remake may not be coming out, though, I thought it would be a fun challenge; it's always a nice challenge to do things you aren't supposed to do. (I got into the blocked-off section of Avernum in Avernum 2: Crystal Souls, for example.) Has anyone done this? Can you do enough damage in one round to R-I before she heals herself?