After un-archiving the practitioner file, you will need to add their column to the appointment book again.
To add a practitioner back on the appointment book you first need to close the appointment book. Then go to the Appointment Book tab in System Information. Select the Columns sub-tab and click Add to insert the practitioner back onto the appointment book. Do this again to add their additional columns back if they had multiple for each extra column.
When you reopen the appointment book you will be able to view previous appointment data unaffected. Archiving the practitioner once more will prompt you to automatically remove the columns from the diary.