There is an option in the system to automatically archive all "Time off" for an employee once they become Archived. 

This will need to be set up by someone who is an Admin user within Natural HR by going to

Administration > Company > Settings > Company settings

In the General settings section you will see an option to Auto archive leaver data including, Time off, Training, Mileage, Expenses and Time tracking.

Select the option(s) for this to automatically happen when a Leaver employee becomes Archived.

Please note: This will ONLY apply to existing Employees who are marked as 'Leavers' and will not impact Employees that were Archived previously.