Final answer:
Mrs. Whatsit undergoes a transformation and sacrifices herself to save the children. The children respond with bravery and determination.
Step-by-step explanation:
In the novel, Mrs. Whatsit undergoes a transformation and ultimately sacrifices herself to save the children. She becomes a celestial being and joins the battle against evil. The children are initially shocked and saddened by her transformation, but they ultimately respond with bravery and determination to continue their quest to save their father.