My understanding is that part of the reasoning for the go ahead with the bombing (and many top military personal/advisors were actually against it) was to end the war quickly before the USSR could enter the Pacific war.
The USSR did not have benign rulers true,
but one simply cannot say for certain how things would have gone had the USSR occupied a part of Japan. If more or less lives would have been lost.
I mean, there has been US interference in the political affairs of post-occupation Japan for many years, via sending money to the LDP helping, if not ensuring defacto one party rule in Japan. And I thought I read something about violent suppression of street demonstrations at some point in the post-war period.
This may sound rather odd, or even extreme but,
A "divided Japan" or a "Japanese archipelago with political boundaries that do not look the same as a map of today" would not necessarily have meant more suffering of even having been a Soviet puppet or satellite. Wasn't there one or two eastern European countries that were not a part of the Eastern Bloc? Yugoslavia was it?
(and I type that not to support different boundaries today, but that only about a century or 2 ago,
Hokkaido and Okinawa were considered like "frontier" [see chapter 5 of
"Multicultural Japan: Palaeolithic to Postmodern"
In Part 2, Chapter 5, Tessa Morris-Suzuki shows how the Chinese way of thinking of one's own nation as the center was taken on in Japan, so peripheral areas including Ainu lands and the Ryukyus were considered foreign until the modern era. The Japanization of the Hokkaido area was a response to the Russification of the Kuriles. Assimilationist policies were later extended from Japan's periphery to its colonies abroad. The Western-introduced idea of civilization (bummei) allowed the periphery to be reinterpreted not as foreign spatially but merely as backward temporally.
So, a different looking archipelago would not necessarily have resulted in a "war of reunification", being closer to the beginning of the modern era that Morris-Suzuki describes.
Of course, all lay-person speculation on my part.
To go along with the bombing stuff,
and wasn't there something about Japan having sent envoys to Moscow in spring of that year (or a year earlier?) to "feel around for peace"...some Japanese prince comes to mind as the envoy?
Of course, the only sticking point was to be able to keep the emperor.
Which ended up being the case anywho.
So a land invasion and/or divided occupation, as well as a-bombing could have been avoided as well.