Going back to what Bakker said:
They had no difficulty killing themselves afterward, and he was their better, so why assume he would have difficulty?
Possibly they presumed he would kill himself. I mean, they did and he, being their better, would too right?
Except what he learned was that exile was not death. He learned he could survive, even thrive out there. So he left instead. The key, to go back to my first post, is that what he experienced outside Ishuäl is the key, not really any specific knowledge.
My brain got fried somewhere along the typing of the post below so logic might be a bit over the place, but I'll try anyway

I'm going to quote this one and mention that I haven't read TUC yet and have not read Jackehehe's TUC spoiler either.
I refer to the chapter about the story of Korringhus's loss of innocence upon starting to kill Shriekers and Singers in TGO:
After an upbringing in a closed environment, such as a monastery, contact with the outside world
will give you new insights.
Pushing forward along an interpretation I had earlier: The Dunyain Mind is bred and brought up to experience only Reason (aka the Logos) to the point of blunting all sense of emotions: There is no love or hate, nothing. They only learn how to recognize these in others during their training, and they can probably recognize them in the defectives, who are definitely Conditioned Ground.
Moënghus then encounters Sranc, which are most definitely Unconditioned Ground, which is important: He starts killing them
Mindlessly, as they'll probably have attacked him on sight/ smell. His training in the recognition of emotions leads him to find out how Sranc emotions work (same as Korringhus), as there is no "cause" for their emotions, and therefore to conclude that Effect does not necessarily imply Cause (and that Effect can
determine Cause), totally opposing Dunyain logic. Explaining this as TTT starting to dawn upon him, is not unreasonable. Also, we received an explanation somewhere either in TJE or TWL that killing eventually has a numbing effect on souls: This is confirmed by Korringhus's story.
This understanding of emotions (combined with the killing) leads to Moënghus being able to reason with additional Probabilities, something the Elders cannot possibly conceive and therefore puts them at his mercy, which in turn leads to him going into exile. I agree that his exile must have been a litteral "going into exile", as opposed to "being forced into exile".
For Korringhus, as I interpret it, the above (assisted by Mimara's Judging Eye) eventually leads to understanding why he
Mindlessly saved "the Boy" from the nursery by finally understanding what "The Interval Between Them" was and leading him to his Zero-God theory.
Note that the "
Mindlessly" in the previous passages is a key requirement for the Enlightenment of Moënghus, Kellhus and Korringhus, as this opens the Mind for other influences. This implies acting without Cause, and therefore an Effect without Cause. The fun part of that, is that starting TGO, we also see the Men of the Ordeal degenerating little by little, likely because of the Meat combined with the dehumanization of crimes, into minds revolving around "Actions without Cause".
I think therefore that the whole chapter where Korringhus recounts what happened up to and including meeting Achamian and Mimara, is in my opinion a direct reference to what Moënghus and Kellhus experienced respectively 50 and 20 years earlier. We know from Kellhus that he received his insight in Caraskand. For Moënghus, the above does not appear unlikely to me.
As to Moënghus's choice for the Psukhê may have been an accident, but it can also have been a conscious choice. Seeing the power with which he wielded other people's emotions, it's not far-fetched to expect greater things from Cishaurim magic. Also, I wouldn't be surprised if he knew more about the Psukhe than we do... Face it, we don't know that much, and I wouldn't be surprised if TUC gives us more information on why the Cishaurim (bar Meppa) needed to be hunted to extinction.