This reminds me on similar things that happens in many, many video games, or manga. Basically something like an army/group that's completely outclassed by the main character that you wonder how they survived that long/what was their plan if the hero never appears. Just example from the top of my head, something like the Rebels in Megaman Zero, who's completely outclassed by Zero and you wonder how they survived before they found Zero, also Sidonia's Defense Fleet before the appearance of Tanikaze in Knight of Sidonia, and something closer to this event in this manga (though a bit more obscure), a certain arc in Shin Tekken Chinmi.

In that arc, the rebels are having this elaborate plan to revolt against the evil tyrant, but despite all their elaborate plans, it still hinges on two things, defeating the evil general of the army and the captain of the guards, who are combat monsters and capable of shrugging hordes of common soldiers like they're characters in a Dynasty Warrior games.

Their plan was splitting the rebel commando group into two, with the smaller group (including the main character) to distract the guards, and the bigger group to capture the evil king (which the general is assumed to be by his side).

After some long and grueling battle, the mc managed to defeat the captain of the guards (the rest of the commando in his team are practically useless and was only there for moral support), and then he had to defeat the general of the army, who turned out to be even stronger and completely slaughtered the other half of the commando team.

So... what was the rebel's plan if the MC didn't accidentally got involved in all this again? It was so ridiculous that it becomes silly . I mean, at least in this current event in Promised Neverland, the rebels actually is pretty decent and managed to do things without Emma.