By taking a look at Yukio Mishima's works, it's reasonable to state that the author not only antecipated the coup's failure but even carried it out EXPECTING to fail, and thus achieving the pretext to arrive at a heroic death.

In his last book Sun & Steel, an autobiographical essay which deals with Mishima's philosophy of the body as a mean to achieve artistic perfection, we find these words:

"(...) Specifically, I cherished a romantic impulse towards death, yet at the same time I required a strictly classical body as its vehicle; a peculiar sense of destiny made me believe that the reason why my romantic impulse towards death remained unfulfilled in reality was the immensely simple fact that I lacked the necessary physical qualifications. A powerful, tragic frame and sculpturesque muscles were indispensable in a romantically noble death. Any confrontation between weak, flabby flesh and death seemed to me absurdly inappropriate. Longing at eighteen for an early demise, I felt myself unfitted for it. I lacked, in short, the muscles suitable for a dramatic death. And it deeply offended my romantic pride that it should be this unsuitability that had permitted me to survive the war."

Mishima was highly concerned about the relation of muscular integrity and having a honorable death, and by the time he commited seppuku, he was a 45 years old renowned bodybuilder and martial arts practitioner. The prospect of dying of old age was a lurking terror and the opportunity to achieve matyrdom was fading.

His intentions are made even more clearer after we realize that the 'nationalist japanese warrior who ends up comitting suicide after a failed coup attempt' is a central theme that fuels two of his most famous works (SPOILERS): the novel Runaway Horses and the short story/film Patriotism.