Estimated Japanese deaths if a land invasion would have occurred?

The professional historian must keep in mind the politics of war. War is the obtaining of a political goal by other than political means.

Casualty estimations will almost ALWAYS have some political influence.

Advocates of the use of the "bomb" (Atomic Bomb) will estimate higher casualties to justify the use of such weapon(s).

Or...in the absence of proof; estimations can truly be "estimates." But politics will not be totally absent.

Japanese casualties have been quoted in history books to be as high as over one million casualties had an invasion taken place. Allied (US primarily) casualties had been estimated from 500,000 to a million casualties, depending upon who was speaking.

Had an invasion taken place, another year or two may have been needed to bring WW2 to a close.

One factor, would not be an estimation; if such an invasion had taken place, many people alive today in the United States (and Japan), wouldn't be here (they wouldn't have been born).