I'm not sure if this is simply part of the original game or if it's something related to CoresixTH.
I hire a janitor/handyman and quit paying attention to him and next thing I know there is vomit all over the place, I look around for the janitor and he's missing. I hire another one, and rinse and repeat they disappear from my work roster.
I'm pretty sure I'm not getting any notifications from them, they simply leave my employ which is quite frustrating having to keep hiring new janitors.