According to scriptural codes, when is a teacher is fit to be abandoned? ( 2.5)

When a teacher engages in abominable action and has lost his sense of discrimination (they took Duryodhanas side because of his financial assistance). Bhīṣma and Droṇa were obliged to take the side of Duryodhana because of his financial assistance, although they should not have accepted such a position simply on financial considerations. Under the circumstances, they have lost the respectability of teachers.