I kind of had two theories: that Syfo-Dyas was an infiltrated sith on the Jedi order, and when he was no longer necessary, Palpatine got rid of him, OR: Dooku was in Kamino saying he was Syfo-Dyas, and then killed Syfo-Dyas some time later, or maybe he was killed by Palpatine by surprise... Why GL didn't make this point clearer, God only knows. If you ask GL about it, he'll probably say "Syfo who?"