There are different kinds of 'ill'. I'm not going to go into details, but someone very close to me has been suffering from psychotic delusions about all kinds of things for many years and has built up an extremely disturbing set of beliefs in trying to make sense of it. She holds down her job just fine, most of the time, and you'd never guess if you met her - as long as she stayed away from certain subjects.
Blagsta may be right that the psychotic breakdown is over, but that kind of experience can leave very deeply held beliefs, particularly if he himself interpreted his breakdown as something else, and if he's experiencing ongoing visions or voices that reinforce those beliefs, he could well be quite high-functioning in many ways and still be 'ill'.