Kevin dies in chapter 24 of Freak the Mighty. Max does not handle it well; however, in his defense, Kevin helped him to believe something completely different was going to happen. When Max shows up at the hospital, he knows something isn't quite right. He can sense there is something different in the way that the nurses are acting. Max asks if Kevin is going to be okay, and the nurse responds by saying that someone should go get Dr. Spivak. Then Max notices that some of the nurses coming out of the ICU are crying. This is when Max tells us that he just goes "nuts."
Someone tries to hug him, and he throws off the hug and starts running. Max tells us that he felt like the little "kicker" he was in the first chapter of the book. He runs through the hospital, ready to hit or kick anybody that tries to stop him or comfort him, and he runs until he gets to the Medical Research building. The doors are locked, but Max punches straight through the glass in order to open the doors. He comes to another set of doors that don't have windows, and he punches and kicks the doors until security arrives, tackles him down, and puts Max in handcuffs.
Dr. Spivak arrives and talks Max through what happened and explains that the "bionic body" was something that helped give Kevin (and Max) hope. The following chapter moves through a lot of time. Max spends multiple days in his room by himself. He's a wreck at school. People offer their sympathies, but Max isn't ready to hear them. It takes until the following spring for him to have processed everything enough and to have finished the book that readers have just read.