The UX of the "Not Returning" section isn't great and the KB article related to it (https://kb.blackbaud.com/knowledgebase/articles/Article/23690) is confusing as well.

In order to stop contract reminders, both the check box must be checked and the date must be entered, but the header of the KB article says "The 'Not Returning' check box will stop Contract reminder notifications from being sent", which implies that the check box by itself will do so. This, however, is not the case, and further down in the KB article it does say that both the check box and date must be entered.

In talking to support it was evident that there are some schools who do use the Not Returning check box but still need to send reminders, so it would not be wise to make the date required if the box is checked. However, it would be greatly helpful and prevent a lot of confusion on the part of both parents and schools if a brief explainer were provided when the box is checked saying that a date must be entered to stop reminders.

Alternatively, a "stop reminders" check box would accomplish the same thing. Our school only uses Not Returning for that sole reason and we track students not returning by other means, so if we had a dedicated check box that would stop contract reminders only, that would solve all of these problems!