Ferdinand starts a revolution that will abolish the distorted royal family and put a true Zent on the throne. Meanwhile, Rozemyne continues to wrestle with divine interference.
To elaborate a little more, he needed someone from the main royal family to open the door to the farthest hall (branch family members like Gervasio don't have the authority for that), so his Lanzenave allies could gain their divine wills. And fooling Hildebrand was just the easiest way to get the door open, and the least likely to give away their ture allegiance prematurely.
Sylvester getting a hint of what that negotiation between Ferdinand and Trauerqual was really like, and how much duress must have been in play... Along with Ferdinand's white hot anger that after all that, the Royal Family still tried to take Rozemyne from Ehrenfest.
Trauerqual, he's had a role to play that is often in opposition to Rozemyne and Ferdinand. The trug was certainly the last blow to him as a ruler. But he's not a bad guy, just someone trying to make things work. Him asking for permission to speak, and then binding Sigiswald, and apologizing and deferring to Rozemyne and Ferdinand, was a nice arc for him. He'll make a good aub of some random unclaimed duchy if he wants it, or maybe better, simply a nice retirement as an elder in one of the kids' duchies.
Considering how he's the only living person with experience in keeping the duchies in check, he'd probably be best as an advisor to Zent Eglantine, which I doubt would work if he's an Aub. Making him Eglantine's head scholar might be a good official designation for that purpose.