If the person is no longer working with us and we don't want them to have access to our company, we simply deactivate them. We can reactivate the person at any time in the future, thereby restoring their access.
In the People tab, open the details of the person you want to deactivate. Then, in the top right corner, click the Deactivate Person button. Confirm your choice in the dialog box.

Deactivate person
In the People tab, select the Inactive Persons view.

Inactive people view
Select the person you want to reactivate and open their details.
In the person's details, click on the Re-activate Person button.

Re-activate Person