He’s been turned. Sylvanas is a smart one. She staged that meeting with the leaders of the Horde in stormsong valley specifically so the Alliance could see it. It’s needs to appear that Baine really did betray her, even though he (unknowingly) did exactly what she wanted.
Derek was chained up in the pyramid of Dazar’alor, well guarded, and in front of all. It would’ve been near impossible for Baine to sneak him out of there. So Sylanas moves him to her own ship, away from the fleet, in open waters, with minimal crew. Even as Baine beats on the crew they say “they were just following orders” but don’t specify what those orders were. Sylvanas baited it and Baine took it. He delivered a ticking time bomb right into the Alliance, and her show of force afterwards allievaited any suspicion.
So how did she turn him? Was he hers all along? Was the process completed before she put him on the boat? Does he even have free will?
I really want to know what the outcome will be. I highly doubt he’ll get to Jaina, but maybe Katherine Proudmoore? The dialogue between Jaina and Anduin suggest he’ll be taken to Cailia Menethil, so maybe she is a target? Could Lady Ashane possibly have a part in all of this too as we are unsure why Sylvanas rescued her?
Tell me your thoughts!
P.S. I believe Sylvanas knew about the attack on Dazar’alor and let it happen. She needed Talanji on the throne. Losing part of the fleet was the price.