While I don't believe Saurfang would ever betray the Horde, I do think he would feel a debt of honor to Varian, and in this case that would include respect toward Varian's son. After all, the debt was incurred when Varian allowed him to reclaim his own son's body. How better to repay it than to respect Varian's son?
Respect does not mean Saurfang would betray the Horde, only that he might look for win-win solutions to the conflict. Especially if he believes - based on his many many years of experience with such matters - that both sides are being manipulated yet again.
To understand Saurfang, you simply have to ask "What does honor demand in this situation?"
Looking at it from his perspective, based on what he knows and/or can reasonably infer.
When you've decided what he would think is honorable, you know what Saurfang would do.