Cereal mascots are still heavily used, on an given Saturday morning or during any part of the day on any of the networks airing cartoons you will see Tony the Tiger, Sonny, the Trix rabbit, The Flintstones, Tucan Sam (and nephews), as well as a number of other cereal mascots on television promoting their brand of morning time goodness.
One mascot I haven't seen for quite some time would be the frog from Honey Smacks, one of my favorite cereals, it feels like forever since I've seen him grace my television screen, there are others too. But as a whole I would say that cereal mascots are alive and well in todays market and aren't going anywhere, or at least I hope they aren't.