Failure in his coupdeta was still a victory. He was able to actually do it staging a hostage, fighting off a few officerd, and gathering the army.
It was a victory because be said he was going to do it through his writings and he did it.
Few people had or have the courage to sacrafice your entire life or future to nationalist over throw of their governments.
Seppuku is often reminiscent of Christian myrterdom. Mishima out lined rather clearly this sense of martyrdom in his essay to America on the subject. With seppuku is is a chance of redemption through dedication of spirit to the ideal you fought for but perhaps lost. You give your life to that ideal or goal. Laying your life down telling the word that such a cause is greater and more true in justice than your own life. It is casting your oppostion out without them taking you as the looser. He so loved Japan to the point he died for the country.
Some say it's harder to live struggling and building Japan than it was for Mishima to kill himself. He got to die whilex the rest had to push onward through the pains.
Sure it is, but it doesn't lessen Mishima's own sacrafice. Sacrafice ng ones self means they won't feel the pain others will endure as they live, but it also means that they gave up every joy of life along side that pain. They gave everything they had, family, emotions, the future, years of life, to their goals.
It was bravery. It was sacrafice. It was a cry to Japan to see what he fought for and grasp it for themselves. It was seppuku.