I think many people are saying there is no redemption possible. Or that even if there were, they would choose not to because he just isn't likable.That's the point here. That's not a reason Zach is the way he is. That's a consequence of what he really is. He's a personification of what a guy shouldn't be. And it's not that he's an ordinary loser who tries to learn from his own mistakes. He's so bad that he doesn't even try to change for the better and take advice of much more experienced mates.
He's got a chance 'to start over' now since the MC's back and could be a pretty good role model for him to follow, but... Zach is incorrigible. There's no excuse for what he is. But he still has a chance to fix some things, I suppose.
That will be the true test of what kind of man he is, right? What he does next.