Yeah, I think that'll come down to how Merrill hides what she's doing from the rest of the team, and we can probably handwave them not pushing her to tell them based on the general excitement of having the Blight-lyrium connection from all their other tests too, like cleansing runes. The mods outlined how the Blight retreats from it, but it doesn't erase it, so cleansing runes aren't a cure and Merrill can keep quiet on her actual cleansing techniques.