Analysis: What's Up With the Ending?
It's a happy one, as White Fang finally gets to "lay with half-shut patient eyes, drowsing in the sun" (25.45) after all the horrible things he goes through. It also comes on the heels of a big ol' climax, as London suddenly drops a crazed escaped prisoner into the proceedings and watches White Fang tear the man apart: "A gaping throat explained the manner of his death," (25.18). So while White Fang may have earned himself a little R&R, it's not like he's gone soft on us.
See, the grand (read: gory) finale with the convict shows how White Fang has benefited from both the ugly side of his journey and the pretty one. He loves his master as no one else and would cheerfully chuck himself in front of a bus for the man. That's something he'd never do for anyone who… oh, we don't know, beat him silly with a club. So he has the self-sacrifice and nobility of civilization to help him defend his master when trouble comes a'callin'.
At the same time, he has the toughness and meanness of the wild to make him a super ninja wolf. He gets the drop on Hall no problem—like sneaking up on a tasty bunny—and goes for the kill like a good killer should. More importantly, he hangs on after getting pumped full of lead, showing a level of perseverance that would impress even the Terminator. If he hadn't been brought up so rough and mean, he might have just surrendered and died. But because he went through the wringer of life, he hangs on… and gets puppies and sunshine (quite literally) as a reward.
It gives White Fang's journey a real Zen quality: even the bad stuff that happens to him helps make him a very good dog. Is London trying to say that bad things make us who were are as much as the good things? Maybe. If that's the case though, then he's also trying to tell us how we can learn from negative experiences and push them in positive directions, just like White Fang who takes down a bad man with help from all the bad things he's learned.