Instead of using the atomic bombs or Operation Downfall, would it have been feasible for the allies to try and starve Japan? They had already cut off Japan's supply lines, would Japan have potentially surrendered if this had been continued?
Short answer is yes.
US fleet blockades Japan, bombers keep dropping bombs on cities. Soviet Union enters war on August 9th. In 1 week the Japanese army is destroyed in Manchuria. Japan surrenders around August 15th (as happened in reality).
Sadly the atomic bombs were probably unnecessary for the surrender of Japan.
This thread gives more info http://www.reddit.com/r/AskHistorians/comments/1y5g5j/what_happened_to_the_japanese_politicalmilitary/cfhmsjv