Lily covers his back, and that lets Geralt know a lot of things about her. It lets him know she's not a total berserker and she has some control over her powers. It also lets him know that she won't let someone she doesn't really care about (him) die with witnesses watching. So she's at least rational and capable of human-seeming decisions. He still has to decide what to do about Lily, and he hopes she turns out to be okay, like Ben. Killing a monster in the shape of a little girl would be painful, and she seems perfectly fine, monstrous powers notwithstanding.

Geralt looks over in time to see Ben slam to the ground and the Witcher curses. He drops the empty beer bottle and wades over to the unconscious werewolf's side. A chipmunk attempts to drag Ben away by the feet, but Geralt stabs it in the chest and the thing screeches as it expires. The Witcher rolls Ben over and it looks like the werewolf isn't dead, just unconscious. Good that it wasn't worse.

"We should get out of here!" he calls to Lily, and he looks up at her. "Ben's down, and I'm worried. He took a crack to the head. He needs water and to lay still."

That was all the medieval medicine that Geralt could offer a comrade with a headwound: laying still, darkness and water. Medieval medical technology was relatively crude when it comes to head injuries.