Expectation of death in combat isn't the same as ritual suicide
Yamamoto himself drew a lot of ire from Japanese nationalists for his own stance on things, even assassination threats prior to the war, and took them in his stride. I don't think he had any fantasies about "going out in a blaze of glory", unlike even many of his subordinates - he just had a sober and realistic attitude about his prospects. And was proven right, mind you.