Package Zen won't delete former employees from your Dashboard because it's extremely common for people to receive items at their old workplaces.
However, you can still prevent former employees from getting Package Zen notifications by replacing their contact information with that of current employees at your organization. That way, someone will be able to accept items on their behalf.
If there's isn't a current employee who can accept items, you can change old employees' contact information to your organization's operational email address.
Follow these instructions to update old employees' contact info.