I wonder how they'll deal with the betrayal. It is true that they lack a lot of men right now. Defending against one or two waves is one thing, but there's thousands of them mongols.
@Grimmycoffee That white-haired leader is pretty suspicious of him already. And the MC has felt the pains of betrayal, considering his reason for exile is because of it. Unless they are literal retards, they may have already discussed how to deal with him in the background if he tries to go through with it and open the gate.