Hi - I'm certain that others will weigh in on this, but my take on this is that they want to be sure they understand the situation before saying that it is okay. I'm not sure I understand the reason you gave for not completing the minor so it's quite possible that the adcom dean didn't entirely understand the reason or immediately accept it. By writing a letter in which you explain the circumstance clearly, it gives them a chance to evaluate the situation and become comfortable with what happened. It is very likely that this will not affect your admission to this school. Still, they need to look at the whole application and be sure that they don't feel like you were not entirely upfront during the application process. Again, the overwhelming probability is that they still will want you, and it is crucial that you are very clear in your explanations. Avoid saying things like "this minor wasn't required for medical school." The school may have felt that it was important in evaluating your application and you should not focus their attention on this issue. I would note that throughout your medical career you will be asked to explain things you have done. This includes morbidity and mortality conferences and even daily rounds. Be prepared for the challenges this presents. Consider this as a chance to learn a bit about explaining yourself and facing a review that will, in all probability, end up in your favor. Good luck and I hope you can have a nice holiday despite this, or better yet, that they reassure you before the holiday!