If a previous employee returns to work at your company, you can re-employ them on Polaris.
This can be done by finding the employees record on staff maintenance - you can view leavers by selecting Filters and choosing "Only Leavers" or "Include Leavers" on the Show Leavers drop down section.
Once you have found the leaver in question - navigate your way to the Employee Movements Tab in their staff maintenance.
Once on this tab, click "VIEW", then press "Re-Employ" and then you will be asked to confirm.
Once this is done, all their personal data will be repopulated, except job type and pay rate which will need to be added - this is because they may be coming back to do a different job to what they were originally.