Yes and no. In theory, the game ends when you gain all the powers available to your character class. You must reach Level 18 to gain all those powers, which makes Level 18 the "end of the game," so to speak. But since you signed the Hero Pact, you’ll have to play beyond this point until your class officially ends.
If you reach Level 18, you’re a Classcraft champ! Pat yourself on the back for all your hard work.