The Japanese were heavily entrenched in their home islands. That did not mean they would never surrender. The question was: what would it take for them to surrender on the terms the United States desired? (Unconditional surrender.) The US was well aware that there were splits on this issue within the Japanese high command, because of the MAGIC decryptions of Japanese foreign communications. The US understood that the militarists believed they could "wait out" the US, making it difficult for the US to invade and thus "bleed out" the US public, which they thought would tire of the pointless bloodshed. The US also understood that the minority "peace faction" was not at all prepared for unconditional surrender, and was attempting to find diplomatic solutions that avoided it (that is, conditional surrender scenarios). These were part of the thoughts behind the atomic bombings. This post goes into much of the timeline.

Separately I would just note that this was not why the US dropped the atomic bombs on Japan. This is a reason given after the fact. But the reason the dropped atomic bombs was that they had atomic bombs and the war was still going on. It wasn't a "well we HAVE to drop these two bombs on two cities within three days of each other or otherwise the war will continue forever." The plan was drop atomic bombs and invade (and see what happens after the Soviet Union declares war). The framing of the atomic bombs as the "central" question of this story, and as a moral "balancing" act, is entirely after the fact, not how it was thought about at all in the planning stages. It is relevant to talk about the US perception of Japanese willingness to surrender, to be sure, but it is incorrect to connect that so cleanly with the "decision" (there was no single decision) to use the atomic bomb.