I do not think that Buck would at any point be able to rejoin man after what has happened. He has taken an amazingly hard path in this book. There were lots of things that could have certainly gone better for him but also could have gone worse. He made do with what he had either going for him or against him no matter what was thrown at him.
I think that he wouldn’t be able to rejoin man because the only thing tying him to man is now gone. John Thornton I believe was the only thing holding contact to man for Buck towards the end of the book. He would disappear for days at a time when the wolves would call him away from the camp. Days later Buck would remember John so that’s what was bringing him back to any contact with humans. But now that John is gone Buck won’t have any reason to come back with humanity. “Man and the claims of man no longer bound him.” Pg. 76
When Buck was in the wild he felt very at home and like he was one of the leaders. “He followed, with wild leapings, in a frenzy to overtake.”Pg. 70 It talks about him overtaking the wolf when he first meets it. When he first meets up with the wolf the wolf runs but Buck follows wanting to overtake. With Buck wanting to overtake this is what makes me feel like he is too far gone now to come back and be able to be a dog again.