William disappeared and went to go look for daisy, because in the good ending cut scene for chapter 6 in book 2 we see daisy holding a note saying something about the military, basically William is going to look for daisy in the military. If you remember, Willow said something about how the military was looking for a cure. I think when we go to the military with willow and the other members, we will reunite Willow with Daisy and William, Save Zizzy, and make enough of the cure for everyone that became infected, and the infection will be gone, no more trouble, no more attacks, no more sad infections of the ones we love.