如果二战日本不主动投降？

迷茫的维修

If Japan had not surrendered after the double whammy of the Hiroshima/Nagasaki A-bomb attacks and the entry of the Soviet Union into the Pacific War, it is likely that:

The 20th Air Force would have resumed its massive conventional bombing campaign against Japan’s cities (including Kyoto) until several atomic bombs became available in 1945 and 1946. (I believe a third A-bomb could have been dropped sometime after August 15, 1945 had the Japanese not agreed to surrender on that day.)
The invasion of Kyushu, codenamed Olympic, would have been carried out on or around November 1, 1945. According to Alfred Coppel’s The Burning Mountain: A Novel of the Invasion of Japan, which was based on the actual American and Japanese war plans for the invasion, the Allied objective was to capture only enough of Kyushu to establish a series of naval and air bases there. These bases would then be used as part of the infrastructure for Operation Coronet, the invasion of Honshu.
Emperor Hirohito and his Cabinet would probably have been killed or held incommunicado by radical militarists who refused to surrender to the Allies. (This is the one element that is necessary for this “no surrender even after the Soviet invasion of Manchuria and the A-bomb attacks” scenario to be even remotely possible.)
For the Americans, it would have been the bloodiest campaign of World War II if the Olympic/Coronet landings had taken place. Based on the casualty figures from the battles on Peleliu, Iwo Jima, and Okinawa, the most-oft quoted estimate of total U.S. casualties (dead, wounded, captured, or missing) cites a figure of over a million. In 1945, the U.S. government ordered 500,000 Purple Hearts in anticipation of heavy losses. To this day (2016), the U.S. is still awarding Purple Hearts from this batch of medals.
Japan would have been forced to surrender eventually. Even taking into consideration the nihilistic world-view of the die-hard hawks in the Imperial Japanese Army and Navy, the Allied onslaught on the home islands would have been relentless. Nearly all of the country’s industrial capacity would have ceased to exist, and the casualties (mostly civilian) on the Japanese side alone would have reached the 30 million mark by the time the war ended.