Indeed. I agree with you, though, that the US government is not capricious. If the US receives an unconditional surrender offer, then they will take it, if only to stop putting US soldier's lives in jeopardy. The real danger, in my view, is that the Showa Emperor's "treachery" will be discovered, and the Militarists will try to appoint the boy Akihito and rule as regents. Things would really come to a head then...
Of course, Militarist Japan was starved into surrender in OTL. I've seen figures projecting more than 10 million deaths from starvation and malnutrition in the winter of 1945 if the war continues. Here, if the US is willing to us gas on isolated island outposts, they can be in a position to bomb and blockade Japan even sooner. I think I've brought this up before, but the most important part of the blockade in my view was not blocking the ships from Manchuria and Korea. It was bombing the railroads in Japan into ruin, and air-dropping mines into the canal network of the Home Islands. That made the cities starve almost immediately, because even the rice in the fields a few prefectures over couldn't be reliably brought to the industrial cities anymore.