japan was getting firebombed and still rejected surrender...in my mind i doubt the Japanese would have surrendered because of the firebombing. They knew that the invasion was coming...and it was...in only 3 or 4 months (from august when we dropped the bombs...but in this case didn't) The Japanese knew that they would be able to hold out until the invasion. And then the invasion would have taken place just as the military planned.
BUT
luckily there WAS a bomb...i doubt we would have just bombed and bombed them when the military already had a plan ready to go and approved.