When you re-employ a leaver in Sage Payroll, you create a new employee record for them.

When you create the employee's new record in Sage Payroll, when you enter the email address for the employee, if it's the same as the one used for their previous record, you're asked to confirm if it's the same person.

If you confirm it's the same person, this then merges their profile and makes their record active again in both HR and Payroll.