Logically, I would have thought an identified target that sudden stopped squawking would be cause for concern, even if only because it would be highly unusual for a commercial airliner to do that and should set a few alarm bells ringing, especially in a post 9/11 world.
If the radar operator had already marked the contact as COMAIR, while it was squawking valid Mode 3, it might have (depending upon autotrack functions used or not used) retained that track classification with nary a peep out of the radar operator who, not being ATC, may not instinctively know where a given COMAIR is headed to on a given evening.
Do you put your sharpest people on watch at zero dark thirty?
