Even if you didn't get the head out the snake's body will eventually "push" the head out on its own similar to a splinter. The head is no longer alive and the body will know what to do when it sees a foreign object. It is not going to burrow itself inside. I don't think there are any species of ticks that can survive on a reptile so I am thinking that your snake was just an "accidental host" from a mammal and would not be able to survive (complete its life cycle) on your snake anyways.