Why would you allow anyone on the air who knows they are about to be fired?
There was a talk show host in my region who was on for years. I thought he was an absolute jerk. Occasionally I would listen to him for a minute or two just to see if he was still a jerk, and a jerk he always was. You could wait two years, then turn him on for ten seconds, and be guaranteed to hear him say something stupid and obnoxious.
Anyway, when the station (owned by Clear Channel) finally fired him a few years ago, they wouldn't let him on the air to say goodbye. They fired him without any warning, and that was it, he was gone.
I'm quite sure they did it that way because they weren't sure he would conduct himself professionally if he knew he was being canceled.