Some things can be learned on your own, usually technical skills. I learned how to root my phone, install custom ROMs etc just from reading instructions online, sometimes asking for help through forums etc. But for more academic based learning, I feel a teacher can never be replaced. While knowledge can be transferable to the digital world, experience can not. A teacher's experience is what enables them to teach students with differing levels of understanding in different ways. While digital approaches are a one-size-fits-all approach, teachers can approach students differently depending on their respective levels of understanding of a given subject. I even prefer to meet with my PhD supervisors for some help sometimes rather then communicate via emails. A discussion between teachers and students can be more stimulating than a student learning from an online course.