Is it permissible to delete downloaded lectures and refrain from downloading more, and was what he did unlawful, given the lack of encouragement or prayers from colleagues and being subjected to harm at the college?

You are not legally obligated to transcribe lectures and provide them to students, nor are you sinful for deleting what you have written from them. However, this falls under the category of doing good, which Islamic law encourages and promotes. Allah (the Most High) says: "And do good that you may succeed," and the Messenger of Allah (peace and blessings be upon him) said: "Whoever among you is able to benefit his brother, let him do so." He also said: "Indeed, among people are keys to goodness, closers of evil... So blessed is he whom Allah has made keys to goodness in his hands." Therefore, do not close a door of goodness that Allah has opened for you, and offer kindness without seeking reward or supplication, for "We feed you only for the sake of Allah. We wish not from you reward or gratitude."