For me as to the first question, I do not believe that Khavi would have wiped out all the elves. For two reasons really, the first being that she doesn't seem to have the hang ups about what makes an elf an elf as Reyak does. The second being that it as all about the palace for her and her tribe, they wanted control of it, they wanted to wrest it from the trolls, nothting there ever spoke to me of the genocidal pull that Reyak seemed to have fallen into.
As far as letting her warriors hack trolls into pieces for fun, that's only seen with Guttlegraw, and he had just killed Khavi's daughter Vaya, and was directly responsible for so many Go-Back deaths. I think in light of that it makes their rather bloodthirsty actions more understandable, not right of course but more understandable. Speaking as a former marine, it's not easy to turn off the adrenaline after it's been let loose.
One thing I find remarkable about debates on Khavi is comparing them to debates on Winnowill or Reyak. The majority of people on this forum are of the mindset that both Reyak and Winnowill are forgivable people (I wholeheartedly disagree on the subject of Winnie, but I think everyone here already knows that), but that Khavi is not. When comparing her actions to those of Winnie I find no comparison. They aren't in the same league, ballpark, hell they aren't even in the same sport folks. As for comparing her to Reyak, well sorry, I find genocide bone achingly bad, but he changed, so that while he's never going to be my fave I can live with him as a character. What in heaven's name did she do that was so terrible in comparison to all that?!?
It's just interesting to me that most people seem to have sympathy for the devil (Winnie), sympathy for the male anti-hero (Reyak), but little to none for the female anti-hero (Khavi). I have my own opinions why, but they are for another time.
I think that Khavi does feel remorse for her actions, but I think that she tries too hard, if you know what I mean. Her drive to better life for the Go-Backs is like blinders. In a way she is almost exactly like Reyak (minus the slide into genocidal meglomania). Instead of him being her shadow or her his, it's like they're the male and female versions of each other.