"Two working days later and they still hadn't disabled the account of a sysadmin. *rolleyes*"
As a sysadmin, I've sat down with management and ensured they disabled that all my accounts and access codes before I went out the door.
For the simple reason that if anything goes wrong later on, I do not want to be covered in any splattering shit. If they want to call me back in, then they can rehire me.
I've only had one employer who actually thought to change equipment administrative passwords. Most simply leave them alone for decades.