Several more million Japanese civilians plus perhaps close to one million U.S. casualties would've happened if Operation Cyclone had occurred along with cities like Tokyo, Kobe, or Yokohama getting nuked also in the autumn/winter of 1945. Operation Cyclone actually involved a two-pronged invasion where we land in southern part of Honshu first, fight our way up through increasingly violent, bloody pitched Vietnam-like battles until a second landing occurred in Spring of 1946 in central Japan to help push our invasion forces even further against Imperial opposition and help beleaguered U.S./Allied forces fighting in Honshu. The British, Dutch and French would've had units helping us in these armed maneuvers, particularly in original Honshu landings. The Soviets probably decide to intervene militarily too by attacking Hakkiado and landing amphibious units in northern Japan.
Face, you and your FIL should be eternally happy "X-Day" never occurred because if one closely examines how fierce, determined and nasty Japanese resistance became as well as fanatical the closer we got to the Japanese mainland and at Iwo Jima and Okinawa, your FIL as well as countless U.S, British and Dutch WWII Pacific veterans who.survived combat and later on married and built successful lives, families and businesses would've never happened. The War Department during the summer of 1945 were making preliminary estimates that any upcoming military invasion of Japan would cost one American lives, perhaps more and the possibility of a short-or-long term insurgency post-war by hardline Japanese militarists or Shinto ultra-nationalists wasn't discounted, either.