When a manager leaves your organisation, and they have employees reporting in to them, this can result in a situation where those employees no longer have a manager. This can affect approvals etc. as the system will not know who to send those approvals to, as well as affecting the organisational chart.
To combat this, when a manager leaves your organisation, the outgoing manager's manager will be the new manager of the affected employees.
This can then be changed later if desired, but does mean that the situation where an employee has no manager can be avoided.
This option can be found by going to
Administration > Company > Settings > Company Settings
On this page, navigate to the 'General settings' section and set 'Auto re-assign employees when manager leaves' to 'Yes'.