Yes and no.

As the teacher, you decide when the game ends, really. For students, however, there's little advantage to continuing the adventure past level 40 as, by then, they'll have unlocked all the powers and have access to all gear sets.

Getting to this level should be quite rare, though! So it might be a good fun idea to celebrate students who get this far.

Student who signed the Hero Pact have agreed to keep on playing until the class is over, so, in reality, the game ends when the class ends, but be mindful that it might be less motivating once students have less rewards to look forward to.