When a production order has the production status Ended, it is possible to delete that production order.
Proposed solution: this should be allowed or restricted by a new production parameter.
When a production order is in status Created, you can delete that production order, which can be a necessary action in the process. But it is very strange that you can delete a production order that has been ended, even though there are references to it from e.g. the sales order line, inventory transaction etc.