We've been on Onigashima for close to a year now, with no end in sight. You mean to tell me this will all just culminate with a defeat and they all start over for another round of agonizing preparation? How would they have the time to regroup, resupply, all while hiding from the enemy that wants them dead? For all the plot armor levied at the heroes right now, while they have a fair shot against the enemy, providing them the opportunity to try again after a crushing defeat would require plot convenience that supersedes all the plot convenience happening now.