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 be forecast.
The Leave Balance Report will extract data for all employees (including terminated). The report includes a Terminated Date column, which you can use to filter on when you can download the report.
Note: You can create a Terminated Team and move employees into that team when they terminate. This will keep them separate from your active employees.