Witten now works on Khovanov homology. No, this is not a mistake. He is working on Khovanov homology. This is incredibly disappointing, for a simple reason: Khovanov homology is related to unification as much as dinosaur hunting is.
In other words, Witten has given up on finding unification - he is now doing pure mathematics.
To be honest, Witten has given up on unification already several years ago, but many hoped that he might come back to it. But now, as an old man, he has definitely left the quest. This is really really sad.
Witten was the inspiration for many people, with his uncompromising search for unification. But now he has chosen to do what he likes most: abstract mathematics that few people understand; abstract mathematics that has no relevance to physics.
That is the sadness of Witten's story: the smartest man on Earth has not succeeded in unification; he is so disillusioned that he left the quest.
Why did this sad story happen? His insistence to cling to supersymmetry, to higher dimensions and to string theory put him on the wrong path. And he was never able to backtrack.
For a really great man, look at Steven Weinberg. In contrast to Witten, he really is backtracking: Weinberg does not believe in supersymmetry any more, he is cautious about the Higgs, he does not believe in higher dimensions or strings any more.
That is the way one wants to grow old: getting rid of your prejudices, and getting nearer to wisdom. Instead, Witten has maneuverd himself into a prison defined by string theory. It will be interesting if he will ever leave it.
Mind you, this is interesting as a human destiny. The ideas Witten is proclaiming are not interesting since decades. What a sad story.
Many years ago, Buber once wrote a booklet around the question that God asks Adam in paradise: "Where are you?" Buber argues that God asks this question every day to every person: "Where are you?" Where are you on your path? Where are you in your life? Where are you in your calling?
Witten is a successful person by every standard one wants to apply. And maybe his calling was to show that string theory is a dead end. But was it really? Wasn't his calling to do more?