This will depend upon who you are using as Registrar for the domain. Some Registrars allow for the changing of Contacts easily, while others, like Network Solutions, can be a real PITA if anything out of the ordinary happens.
The one absolute though is that the actual Registrant for the domain is correct because they are the owner. If all else fails, the Registrant, or the Registrant's legal representative in the case of organizations, can contact the Registrar and get things sorted out.
As for just general Admin Contact for any domain, in an organization that is so susceptible to change, you just need to be sure that the Contact is the person who will receive notifications from the Registrar. It does help to have a permanent e-mail address for the Admin Contact. In other words, whoever comes in to take the place of the Admin Contact will always use the same e-mail address, such as
admin@your-domain.com, or whatever. That way it doesn't matter who the person is, or how often the person in that position changes, as long as the e-mail address for that position always stays the same so the Registrar can send e-mail for renewal notifications, etc.