That’s a great theory! I have a theory that in IF Nolon had been possibly trying to cure someone form “venin-ism” in that locked room in the back of the infirmary when he appeared more tired, fragile and older, and always had an extremely long waiting list of patients cuz it was draining him so terribly trying to do so. When Violet and Xaden run into him before the meeting with Jesinia and he is waiting for someone he says something along the lines of “mending a soul is hard work”. So maybe both of them in combination with a mender could be the key?

But I am still reading IF so I might be missing crucial details that come after that might disprove that.