Yeah, this was very much a very partial victory for Tyuule if anything. There was some harm done to the empire, no doubt, but they live in an old world where a human life is only so valuable, so in the bigger picture it's no big deal. Zolzal suffered a miserable fate, being reduced to a paranoid weakling with high infamy, so that's at least something for Tyuule. In that sense maybe I'll have to take back my earlier words: It could be more cruel to leave him alive. Unless there's a critical situation where he comes again for her for advice and then she could betray him in a grand fashion (if you can even talk about betraying considering everything she has done so far is to hurt the empire).