He goes on to live in the care of Ben, Marika and Evan. Sam ultimately survives the 5th Wave thanks to his sister's sacrifice in destroying The Others' spaceship.
He has shaped himself up into becoming a hardened young boy with their changed world. Over time he was reunited with his sister and they, along with the squad, head out to survive against the Others. He was taken by the Others and begins training for their children army as the 5th Wave. He went to become the youngest member of Squad 53 and became quite close and loyal to Ben Parish/Zombie. Unknown to him until much later, he lost his father soon after with the emergence of the 4th Wave. Sam lost his mother in the 3rd Wave and was then separated from his father and sister.
He is Cassie Sullivan's little brother and her only living relative. Sam is one of the survivors of the waves sent to destroy mankind. Sullivan, also called Sammy and Nugget, is one of the main characters of The 5 th Wave by Rick Yancey.