Completely stuck during The Impenetrable Cage

When going through the tunnels after getting the key from the refugee, I sent all my heroes through because nothing was advancing.

Now, only two came out. When I press the button to select any of the two vanished heroes, the camera goes to the tunnel's exit.

I can't advance the quest or exit to world map because in order to do so, I need to gather all my heroes together.

So I'm completely stuck, game over.