Can you point out the line where a teacher relinquishes the role of a learner?

Its a very tricky situation. I don't know if a quantitative answer is available for it, but a philosophical answer is up for debate. Can a teacher stop learning while still being a teacher? As time is a moving constant, it is nearly impossible for a teacher to not learn and evolve and still able to provide best education to his students. One must keep learning if he/she wants to teach in best possible way.

So finally, to answer your question, I can't think of a situation where a teacher can stop learning, unless his knowledge makes him arrogant enough to think that he does not need anymore learning.

I do not think such a line is drawn in education.  Learning is a dynamic activity and the role of the teacher is to continuosly engage the learners pushing them to acquire the taste for learning.  My view is that a teacher is always encouraging a learner to move towards a situation where he/she creates a apetite for learning.  Therefore the teachers involvement with learners is an endless process. 

"Teaching" as an activity does not exist: or at least it is meaningless to think about it in isolation. There is always an interaction between the Teacher, the Learner and the Subject being taught.

 This is not a wholly banal point, because;

• The Subject is not neutral: it imposes its own discipline. Early mathematics is linear, for example, because you have to learn to count before you can do anything else. Some other subjects allow you to sequence the curriculum with more freedom.

• The Learner has her or his own attributes, motivation and baggage, and these may or may not "fit" with the subject and/or the teacher. The Learner is usually also part of a wider class group of other learners, which may help or hinder (or indeed be irrelevant to) the learning process.

• The Teacher, too has her or his own values, preferred approach to learning, history of learning the Subject, and level of skill.

• All this takes place within a Context, which may define the reasons for the teaching-learning (compulsory schooling and the National Curriculum), the desired outcome (expressive, as in "learning for its own sake" or instrumental "I need the qualification for a better job"), and the power relationship between the Teacher and the Learner(s).

I can't think that there is such situation cause teaching is an exercise of love.

This is indeed very interesting to note, that a teacher is a lifelong learner. At no point can one give up on learning. It is not only the bookish knowledge that one has acquired has taught one. For a teacher, he/she has to keep his mind and eyes open. One learns from once surrounding, so the very surface one moves on is a blackboard of learning he /she has embarked on.

As an eduactor we never stop learning either by prusuing higher education for our professional growth or learning from our students as well. Teachers everyday discovers something new about the feelings and attitude of learners in dealing with it we as teachers also develop and reflect upon our sense of compassion and empathy. We became more humble and humane because of the learnings and realizations we get from our students.

Short answer: A true teacher is forever a student.

This can only happen in case of death,or when the teacher runs mad. An insane person does not have anything to learn anymore in life because the substial niagra of such person has lost coordination. But for a sane-minded teacher, he will always learn because every human being learn everyday even from students.

A teacher is a learner first and after learning the subject teaching the subject. So where there is the end of learning a subject (practically no end), starts the role of teaching.

When we see a question from a differnent angle we learn because we had not tried to see that point of view. Now the question compelled a teacher to think from other angle.