I am writing this as a retired healthcare security officer. We had 1300 or so employees. Our policy was to remove access as soon as possible after the individuals’s last work day. If the separation was unfriendly, HR would set up a high priority task that was taken care of immediately. Policies like that are probably overkill for your situation. I still think that you should remove access on the person’s last day, but that could be negotiated with the individual. If they are taking a call to another church or school, they probably want access to lesson plans and related documents. In the unlikely event that a person gets terminated, definitely remove access as soon as possible.
Jim Sehloff