So I’m reading Revenge of the Hope, which tries to untangle the complicated mess that Lucas got himself into, and would care about if he thought about the canon as much as the rest of us. It’s a quick entertaining page if you care at all about that.
I’d like to offer one possible alternative to this, however:
When they reach Yavin, Han decides to take the money and run and Chewie decides to go with him. Looked at in cold light, it’s for the good of the Rebellion. Even if Yavin is destroyed, there’ll be one agent who knows what’s going on who can try and put something back together, but he doesn’t feel good about it. When Han decides to turn around and join the attack, Chewie is all for it.
I believe that leaving initially would be part of Chewie’s plan to get into the battle without showing his hand to Han. Han wants to leave, and won’t listen to any argument, so Chewie gets him away from the pressure of the situation to work on him alone. You’ll notice it doesn’t take him long to convince Han, I’m sure he always knew he could, and they’re back in the game.
As strategic an asset as Chewie is in the rebellion, I think he knows that this is a pretty big battle. Yoda’s still around, somewhere, to rebuild the alliance if they fail, but there’s no way he can sit out the battle for the Death Star.