"Emperor
Hirohito's tour of the destroyed areas of Tokyo in March 1945 was the beginning of his personal involvement in the peace process, culminating in
Japan's surrender six months later"
"Contribution of Major Fire Raids Toward Ending WWII" p. 38. Turner Publishing Company
Simple, japan would end surrendering anyway, the firebombs caused more damage to the japanese industry and morale than the nuclear ones, unless of course that hardline coup succeded in 1945, something that was unlikely