He compares schizophrenia to insulin dependent diabetes, which can be very scary if someone neglects to take insulin, and so would it be scary if someone stops taking medications for schizophrenia. The reason is that without medications, there is the likelihood that relapse will occur, if not in a week, it will in a month or two. With each relapse, the base line functioning goes down, and Dr. Zimney points out that brain cells can be killed, which will never come back.
Medications, even with their side effects, is the only treatment for schizophrenia which has been shown to be effective.
That said, rehab options and case management options are an important part of treament. (My addition.)