I'm not as sour as most, but he definitely got up and walked out with his job only half done. Where I differ from most around here is that I can't blame him for doing it - I wouldn't work for 1/3rd of my worth, either... and I certainly wouldn't do it in a job I hated, away from the people I care about.
One can speculate until the cows come home about where we'd be if he stayed another couple of years. I think he realised the job was too big to get done in the timeframe he wanted to give, and so rather than half-arse it or continuing to do the job, knowing he wouldn't finish it, he walked away when he had the chance. I can relate to it, and I don't hold it against him.
I really hope he writes a book about his time in Newcastle, I think it will be quite revealing.