Sage HR is advising that you can re-hire a previous employee using the same email address and when uploading their new payslips you have the option to replace the payslips in the employee's existing terminated Sage HR profile. This doesn't delete their old profile and you won't lose their Sage HR data.
Tried this today and it didn't work got the error message saying that the email already exists. Not sure how the leave date would be removed in Sage HR to make this employee an active one again. After speaking to Technical Support, they have advised for me to delete the previous record totally out of Sage HR.