See also Germany post-World War One: the other side (as a collective/society) not only has to be defeated they have to accept the fact they were defeated.
This was one of the hindsight things that I've heard said about Japan post-WW2: it may have been 'fine' to allow Hirohito to stay on as Emperor in 1945 and for a few years afterwards, but at some point the Japanese leadership should have been tried, and this includes Hirohito: he should have had to abdicate and then be tried.
Yes, exactly.
The instrument concluding Germany's surrender, nominally ending the First World War (and for which my prior use of the name is metonymous) is known to history as the Treaty of Versailles [1]. Its terms were notoriously punitive largely at the insistence of the French, who regarded themselves with some justification as having paid the majority of the victory's cost, and Germany was denied any participation in the negotiations which determined the surrender terms to be imposed.
Combined with the Dolchstosslüge ("'stab in the back' lie") serviceably excusing the military failure and logistical collapse which made further hostilities impractical for Germany to pursue, thus leaving no options but to sign or be occupied, so were the conditions laid for "World War 2: The Sequel," as of course eventuated in practice. The actions taken with respect to the defeated powers thirty years later were designed with enormous and successful care to avoid a second, nuclear-armed, repeat. In this connection and as minimally an example of earnest intent, consider the so-called "Marshall Plan." [2] (Therein also see 'Aid to Asia' within 'Areas excluded'.)
I conclude that to have left the Imperial flower intact through a negotiated surrender would have led in about a generation to a dangerously resurgent sense of revanchism, which if prevented would only be so because if not occupied by the United States, Japan would have faced Soviet conquest (remember Tsushima!), which famously left no flowers of any kind intact anywhere within its reach: they would have a constant and enormous problem with civilian misbehavior, no doubt resulting in collective punishment, but would succeed in keeping the victim off the world stage. But I'm very confused as to what sort of terms you think could have been achieved by either Truman or Hirohito, in the absence of the demonstration strikes whose necessity you discount.