Has any station ever faked a firing in the way you suggest, right down to the DJ being "fired" tweeting a heartfelt farewell to his listeners? That would be a "work" worthy of WWE's writers! In fact, that sort of thing has gone on in professional wrestling for years: Wrestler is shooting a movie or needs surgery or is getting married and has a long honeymoon booked? No problem! Just tell the fans he's been "suspended" or have him lose a "loser leaves town" match, then write him back into the picture a month or two later.
Mr. Gleason would know more about this, but I think there's been an April Fool's stunt or two where this happened.