Lea might not be mind-control resistant, but he is stubborn and may eventually be able to will himself to see past the illusions. Either way, he's going to know that something seriously fishy is going on, because the illusion-situation makes no sense given what they know.

He'll definitely be trying to help get people to evacuate and watching people's backs as they do. He can also provide fire for light, warmth, and cooking if need be.