While it may be true that Pirsig's mental breakdown had nothing to do with what went into the book, the facts you have presented here do not particularly support that conclusion.
If his mental breakdowns had been, say, in 1976 and 1978, that would have supported it much better. But someone working on the philosophical underpinnings of a book for over a decade before the book is published is not at all unreasonable.
My primary memory of the book is that the author specifically ties together the quest for meaning and the loss of mental health, even within the book itself.
If his mental breakdowns had been, say, in 1976 and 1978, that would have supported it much better. But someone working on the philosophical underpinnings of a book for over a decade before the book is published is not at all unreasonable.