I got laid off at a previous job and they asked me to stay on six months to train my replacement(s) and finish my project(s). In return I'd get my normal severance and a significant bonus for staying the whole time. I did so and worked hard for the entire time. A few months later I got lunch with my former manager and they informed me they would have absolutely coasted the entire time. In hindsight, I'm not sure why I put the effort in. Live and learn, I guess.