It's up to you where you want to keep your Blaziken. If you're restarting Sapphire then, by all means, trade Blaziken out. Other than that, does he use Return? It can be a pain to re-raise happiness, so there's one reason you may not want to trade him. It's your game. We can't decide what you want to do.
About the gameshark: that's why I don't use them. What probably happened is that some cheat you used changed the way the game loads/saves data such that the modified load/save program works with modified game data, but the unmodified load/save program can't load the modified data. RAM-modifying cheat devices (such as gameshark) tend to have random, unwanted side-effects like this, since the same locations in RAM tend to be used for more than one purpose. All I can advise them to do is evacuate anything important from their games and start over.