When an employee is terminated, leave balances are retained on both the employee record in MicrOpay and the employee profile in ESS. However, the leave won't accrue or forecast.
The Leave Balance Report will extract data for all employees (including terminated). The report includes a Terminated Date column, which you can filter on when you download the report.
Note: You can create a Terminated Team and move terminated employees to that team. This will keep them separate from your active employees.