Hi Ale,
I agree with Akanksha on creating master data with time dependency.
In bex query you can use the filter condition valid to date to 31.12.9999 and it should solve your issue.
You con't delete the employee who left the organisation because transaction data may already been loaded. Why would you delete the employees who left the organisation and is there no data retention period?
Thanks,
Shakthi Raj Natarajan.