Failing the leve will let you re-attempt it next cycle (along with the new one). Of course the problem here is it requires a trip to town to pick up the new ones, and if you do it from each city, it can get annoying.

Basically you fail the leve, complete it next cycle, go back to town and pick up the new leve, fail that leve, complete it next cycle, go back to town and pick up the new leve, fail that leve, and continue the cycle; it's common practice to do this with big SP leves on DoW/DoM classes.