On-Leave
Your staff & volunteers can be placed on-leave as required by setting their 'status' to 'On Leave', and optionally including the date they are expected to return.
Returning from leave
Prior to their return, the system will email those on-leave a reminder they are due to return from leave shortly, and automatically set their status as 'Active' on the date of their return.
You can of course change their status back to 'Active' at any time, or change the date of their return if their circumstances change.