You're a Tengu.
Your whole race gets kicked out of your homeland (Cantha) by a Human.
Do you really want to teach humans now the art of Assassination and Ritualism?
Doubt about teaching other races as well, since you'd be pretty peeved at that stage.
People can worship whoever they want, but they do draw their magical powers and strength from that professions God.
Like Monk's use the healing of Dwayna and the smiting powers of Balthazar. Aside from drawing those powers, they have the free will to follow a different god's teachings (Example Melandru, preserving nature and the like), just not use their powers (Because you can't go Mo/W/R).
Elementalists and Dervishes have free will in this. As they use powers from all the Gods.
I do not know which class will stay and which will go.
Some classes might merge into one. Like Assassin and Ranger into a Rogue-like type of profession.
If we look from a lore-only perspective, Paragons would be logical to still be around just not anymore in big numbers after Palawa Joko's conquest of Elona. Only the majority of his evil sunspear army and a few stray sunspears who have escaped his wrath. The rest were most likely killed. Same might go for Dervishes. However, the Norn might keep the Paragon class up and living, being hunters since birth and favoring psychical-damage-dealing weaponry.
Ritualists and Assassins will most likely survive. Since we recently discovered the Charr even use it. Assassins will still be a great asset to mankind's survival if they're still at war. Monks, Warriors and Elementalists are the "holy trinity" of every game. Necromancer might end up merged with Ritualist. The mesmer is even seen in Nightfall as a Performer-class. Like Bard's. I really have no idea what'll happen with them. Their originality of tricking the enemies mind might be key with them staying. I really have no idea.
In the end, it's all up to Arenanet anyways.