I think the problem with questions like this is that it seems to underrate the complexity of learning and teaching. I was homeschooled until college and the vast majority of my learning before college involved me working through books and watching video lectures alone, but individual comprehension efforts are only one part of a holistic learning effort and you still need peering or someone to ask questions along the way.
Before college, I would say this isn't as important due to the ease of learning pre-college concepts, but at the college level I think peering is important for developing deep, thorough comprehension. You simply need someone to converse with in a natural, humanistic way that is able to provide more insight in to a topic whether this person is a teacher or a fellow peer. So unless human level AI is developed, we can't fully expect to replace the concept, but I think we can certainly change the way learning and teaching is conducted.
Lastly, sometimes I wonder if teachers are needed at younger levels like grades 1-5 as anything more than just facilitators or babysitters. It would seem like technology could replace a teacher at this level simply because of the nature of the concepts being so simplistic. I could see children in the future going to school (or heaven forbid working from home) and working in some holistic learning sim for 3-4 hours a day with maybe 1-2 teachers overseeing progress for like 150 kids. My wife used to be a 5th grade teacher and the amount of fluff time spent trying to get a class to learn a simple concept or fact was just mind blowing to me.