There was a documentary on ESPN about him a couple years ago. It was filmed over a period of several months and you could see his physical decline as the program went on. At the start, he was at a therapy session and was having the "dropsies" playing some marble game. He asked the therapist if there was any hope and she just said things like the games he was playing can only delay it, if at all.
Later they showed him driving and he had special grips on the steering wheel and at the end he needed help getting dressed. In one scene, he is visiting another ALS patient who is in the end stages. He was in bed and had to talk with a machine (like Steven Hawking uses). The guy was telling Kevin to fight the good fight, but that had to be tough for Kevin to see that, knowing that was the fate that awaited him.