Without the shock of the atomic bombings there would almost certainly have been more Japanese civilians dead before the end of the war, even discounting a landed invasion. By late 1945 the allied bombing campaign was sufficiently geared up to destroy entire cities on a recurring basis. It was as effective as the atomic bombings, it was merely a lot less efficient (hundreds of planes and crews instead of just one). Had Japan held off surrendering, and had that conventional bombing campaign continued much longer the destruction would have been far greater.

Had the allies then lacked the courage to mount a landed invasion and been satisfied with a negotiated peace instead of an unconditional surrender, Japan would have become a devastated country with few allies and many enemies, it would not have been rebuilt with foreign assistance and would almost certainly be a 3rd world nation or perhaps even a failed state today.