The metaphorical “what if we killed Hitler before he became Hitler”
In studying history, we are restricted by practicality to study only such things that concretely happened. Surely this leads to something like survivorship bias, so we could be placing undue scientific emphasis on things which were unlikely given material conditions, yet occurred nonetheless.
Therefore some level of speculation is necessary I think, in order to learn from the things which went right due to the non-occurrence of events. Like the eternal dilemma of system admins, the proof of their usefulness is nothing happening, things not breaking, which in turn appears as proof that they were unnecessary in the first place.
Best I can come up with is the handful of averted nuclear deployments during the Cold War, but those are fairly well known.
There was that one time the Soviet early warning system malfunctioned but some brave comrades chose not to launch.
Or that one time that a plane crash almost nuked North Carolina.
Essentially if the many worlds hypothesis is correct, the multiverse is littered with the charred remnants of mid-century Earths where luck didn't go our way.
The 1961 Goldsboro B-52 crash would have totally prompted a "retaliation" strike from
if the bombs went off, wouldn't it?