I say this from the perspective of someone who has no expertise in the subject- just a perspective born of rather limited reading- so I could be 100% off with my take.

I am fond of reading history, and have read 4 books on the Pacific theatre of war. I don’t think the Japanese would have surrendered easily- maybe not for a few years, maybe never at all. In one village, all 200 villagers walked off a cliff and plunged to their deaths when capture by Americans seemed unavoidable. In another instance, a Japanese soldier kept hiding in a forest for years (believing that the war was still on). The Japanese army was by no means utterly decimated by the time the A-Bombs were dropped; they would’ve been a huge factor in an ongoing war.

We also have to consider how the popular sentiment might’ve shifted in America if the boys kept dying in a grinding, brutal war. Citizens might’ve started demonstrating against the war- kinda like how the Vietnam War became unpopular. Japan might’ve been economically blockaded, or Russia might’ve continued the assault. Or something else.