What do I do if staff are resigning in the final week, but the period end date falls after pays are processed?

Create an additional payroll calendar and manually load and edit their timesheets in Payroll HRM > Payroll > Pay Run Preparation > Timesheets.

Information

If their timesheets are still loaded (as automatic pays are ticked and permanent pays are defined for them in Payroll HRM > Payroll > Employee Information > Employees. Click 'Edit' on the employee and open 'Permanent Pays' tab clear their 'Normal Envelopes', add the pays and finish the whole pay run as normal.
Manual pay reduction may also be required if the permanent pay cycle doesn't align with period end date. This can be edited in Payroll HRM > Payroll > Pay Run Preparation > Timesheets.

This can be achieved in bulk through Payroll HRM > Payroll > Pay Run Preparation > Timesheets.