While a sabbatical year might be very beneficial for the person taking it (for the multitude of reasons mentioned in the article), it can be detrimental for the organization. For example, if the person taking the sabbatical is in charge of (or playing a lead role in) a project that is time sensitive, then this is a big setback for the project. Similarly, if the person is mentoring someone else (who is dependent in some way on his presence), then taking a sabbatical is unfair to that mentee.
This is why it is important to plan the sabbatical year so that it is personally beneficial and also not detrimental to the organization and its people.
I'd say that it is just as important to an organization to learn how to deal with people leaving. It's better to have someone leaving under good terms than bad, and if you're totally reliant upon a single person doing a single role, you're not displaying too much 'organizing' in your organization.
This is why it is important to plan the sabbatical year so that it is personally beneficial and also not detrimental to the organization and its people.