Perhaps he realised that he was not physically able to perform in the upcoming 50 dates, that his enormous legacy would be ruined by his sad failure at the 02 arena,
unable to dance or sing properly, unable to give the crowd what they want, ruining his life's work by being a shadow of his former self. Think about how distressing that failure would have been for him, and how people would turn on him even more if he pulled out.
At least this way his legend is preserved.
I don't know, something to think about, it seems strange he should suffer a heart attack to me
RIP Always MJ