I don't see how disgruntled ex-employees would be a risk if the correct policies are put into place like, you know, the whole confidentiality and nondisclosure agreements.
You just did describe a new problem and process. If you have someone on staff you can watch him closely. On the other hand "exit day" brings complications ... especially for sys-admins.
Edit: and so it wouldn't surprise me if a government department with huge budget tended to accrue employees over time. The "easy" path is retention.
