> "Whether the Japanese surrendered when they did or surrendered a couple months later, though, Japanese surrender was largely expected at that point."

By whom? In actuality, both the US and Japan were planning for a long campaign on the Japanese home islands: https://en.wikipedia.org/wiki/Operation_Downfall. The Japanese intended to prolong fighting as much as possible to force the US to abandon the invasion because of mounting costs and casualties.

Even the night before the surrender, some among the Japanese military attempted a coup to prevent it and continue the war: https://en.wikipedia.org/wiki/Ky%C5%ABj%C5%8D_incident