The first two risks are unchanged, a failed and recovered Little Boy always carried the same risk. Three, what if they ignored the bombings? And four I think you misstated, but how do we know a single more allied soldier didn't die because we dropped it on a civilian target?
The first two risks are only unchanged for a demonstration that was not announced to japan, and IMO a demonstration of a nuclear bomb without telling Japan to observe it would not have been effective.
After the bombing of Hiroshima, Suzuki stated to the press that Japan would not surrender, which suggests to me that bombing the middle of nowhere as a demonstration would probably not have persuaded the Japanese government to surrender. Why would a non military demonstration have been more impactful than bombing a city?
Politicians tell bullshit all the time. If they say they will surrender in a week, it's very hard to convince the cannon folder to continue fighting while they negotiate some kind of amnesty for the top level generals.
I've read "The Making of the Atomic Bomb."