Yes, it's a assumption though if they had planned to surrender they would have done so while cities after cities was napalmed with more than half a million life lost (once again a causality rate higher than what was encountered in the atomic bombing of Hiroshima and Nagasaki), nor will they start training civilians for warfare and ignore a final ultimatum to surrender just before the atomic bombing.it is anybody's guess whether WWII would have actually dragged on.. actually..
who knows? maybe without hiroshima and nagasaki the japs would have surrendered anyways.
Even after the atomic bombing, the military oriented Japanese government was still insisting on negotiation in the terms and conditions for surrender had Emperor Hirohito not personally intervened.