If they failed (SPOILERS)

If the class got to graduation and hadn’t killed Korosensei, the barrier never existed and he never fought the other reaper or anything.

Do you think he would’ve let the students kill him anyway so they still again get the reward money and their efforts aren’t totally in vain like he does then or take the risk he wouldn’t explode and continue to teach/help class 3E through life or go do whatever he wants