So - after reading what happens at the Battle for Lord, and how Sylvanis and Saurfang part ways, I think I see where this might go.
No way Thrall is going to let Saurfang be cast aside.
My prediction:
It turns out Sylvanis is still corrupted by the Lich King, and is being taken down a dark road.
Thrall returns to unite everyone against the final baddie and reminds the Alliance he can always whoop them when he gets the desire to.
He and Malfurion agree they could fight each other and destroy the planet, but work together for the common good.