It's OK, picking Hermosa is the right choice anyway, because you can keep a
book of +5 skills. If you chose Kenneth, you need to give it up to upgrade your arena fully
.
I'm going to bump this up because I just played a game where I DID pick Kenneth as my trainer, and I STILL couldn't figure out any way to free Saul. I was forced to murder Saul, and that did resolve the quest, and I'm glad that's an option, but I still don't know the right way to do that.
I got the quest from Kenneth, talked to Tillian, accepted the quest to kill Saul, mind-read the guard, unlocked Saul's cage, then went back to see Kenneth. Kenneth told me to mind-read the guard... but I already did that to get access to Saul, and I couldn't mind-read him again. Kenneth, Tillian, Saul, the guard, nobody had anything to say that would help me adjust the teleporter, so I ended up choosing the "take care of you" option, which initiated combat with Saul.
It was funny telling Kenneth "bad news he's dead", and Kenneth said "oh well, at least you tried to help!"