The following encounter seems to occur only after the events of Now or Never. I'm not sure if it triggers if you don't help Triss because I always help her.
In the Novigrad Docks area, in an alleyway near the ship you take to Skellige during Final Preparations in Act 3, you can encounter three Witch Hunters interrogating two of the King of Beggar's (KoB) henchmen. Interestingly, the hunters know Triss works for the KoB, and order the henchmen to tell them where she stays. When it becomes clear the henchmen do not know her location, the hunters demand the name of someone -- anyone -- who could be associated with mages. One of the henchmen gives up the name of a man who supplies ingredients to mages/herbalists. The other henchman seems appalled at this, and whispers to his comrade that the man has children.
Anytime during the exchange, Geralt can initiate a fight with the Witch Hunters by performing an aggressive action. This is the only way to start the fight because interacting with the group does not trigger a cut scene where you can carry on a dialogue. The KoB's henchmen will run away during the commotion. Be aware that the witch hunters are marked with a red skull, and are therefore at the same high level as the random guards/hunters standing about the city. However, they do drop loot (swords, bolts).
Despite its brevity, I found this encounter quite interesting because it gave a glimpse into the background "politics" that are seldom shown in the game. One, Triss was literally surviving on luck and borrowed time, and was much closer to being caught than she or Geralt thought, even during Now or Never. Two, ironically her downfall, as well as the deaths of her fellow mages, would probably come from information extracted from the lackeys of the man they were paying more than 80% of their profits to for protection. Three, the KoB's confidence (arrogance) in believing that his grand plan with the mages would ultimately grant him control of the city was naive and foolish. He did not consider that the Redanians/Witch Hunters could easily turn or intimidate his people with money, personal harm and/or harm against loved ones.