Max Hastings certainly doesn't think so...

Basically, based on the "To the Last Man" attitudes displayed on Iwo Jima and Okinawa, as well as the strong influence of the Japanese military elite desperate to save face by forcing the Allies to offer terms--in direct contrast to their doctrine of demanding unconditional surrender--Hastings argues that Operation Downfall would have been an immense undertaking, and that the Japanese would have put up strong resistance.

It's been a while since I read the book, and I only remember the broad strokes, so you'll have to read it yourself for more details.