In order to assess brain function, they do a test called an EEG, it measures brainwaves and activity.They would have to have one around the beginning of this, or now, and another one later. This will tell whether your cousin is progressively worsening or improving.
There is not enough information that you give to even guess. You will have to lean on the medical professionals who see him daily and the tests that they do and make decisions accordingly as they present themselves.