Interesting point. I don't know. Some thoughts:

I still think that there's a place for teachers. I agree with richard_reitz that individual attention is overrated. That if lessons were good enough there'd be much less of a need for teachers to diagnose holes in students understanding and tutor them. And that there isn't really too much individual attention in todays system anyway.

However, I think that even with these great lectures, there will still be holes in students' understanding, and that using a human is the best way to diagnose and address them. Like Sal Khan has talked about, I think that if these lectures were available, it'd actually free up teachers to spend more time providing personalized attention. I suspect that there's enough of a need for this such that teachers will still be employed.