If somebody is going to abuse their accidentally-retained access after being removed from my organization, than the incompetence was in having that person in my organization in the first place. It turns out they were perfectly justified in removing him!
First of all, it's criminal, and second of all, it absolutely lights a torch to any credibility they have. I expect people don't want to become unhireable.
I've had access/credentials to organizations that I've left and never abused them even once.