I don't know.

Could Hirohito (Suzuki, etc.) have been convinced by bombs dropped elsewhere?

(our physicists were able to back-of-the-envelope; should their physicists have needed hundreds of thousands of civilian deaths to calculate what an A-bomb could do?)

So I think it's not obvious (multiple books have been written on the subject) what could or should have been done or not done back then; now, from my point of view, those cards have been dealt, for good or for ill.

But was it really obvious? From what I can tell, much of the nuclear arms race happened thanks to espionage. Had information on warheads and the like been properly contained, maybe other countries would not have so easily developed the bomb.