In the "Days of Our Lives" documentary Roger states that John had a mild drinking problem in and around 86. Roger also said that John would have his personal cocktail bar behind stage and the roadies would make him drinks during the show. John was drunk and he through his guitar.
It's amazing to think that effectively that was it for him as a touring career, apart from a couple of live shows, and so he was basically retired by the age of 35. Even after the next few albuns through to Made In Heaven, he was finished by his early forties. I suppose he wouldn't have known at the time of the Magic Tour that it would be the end of his career (self imposed I hasten to add) so he clearly had other demons he was working out at that point too. He certainly seemed a lot more composed and relaxed by the time of The Miracle, so the end of the Magic Tour probably came at the right time for him.
I understand why he retired. I do not understand why he did it this way. No interview, no press release, nothing. Suddenly he was gone. It's also a shame he didn't cooperate making the documentary. His story is as interesting as Brian and Roger's. I would love to hear his side of the story. About how he blended into queen in the '70s - and faded out in the 90s.
About '86 - There were a lot of rumours about Queen splitting up. There had been many arguments. And there was something wrong with Freddie, although nobody at that point could tell what it was. John was thinking "this was it", and in a way - it was.