There's a famous Twilight Zone episode about a time-traveling assassin who kills baby Adolf Hitler. The episode concludes that nothing really changes, as another child growing up in that environment becomes just as bad as an adult.
I'm not sure if I believe it, but it's an interesting argument. There almost certainly would have been people in most of those positions, though perhaps not with the same quirks.
That's what I was trying to differentiate in looking at the list...the impact of zeitgeist relative to the butterfly effect. http://en.wikipedia.org/wiki/Butterfly_effect
In other words, it is likely that Dole [had he won the Republican nomination] would have defeated Dukakis as readily as Bush did in 1988, or that Carry Grant could have starred in The African Queen.
On the other hand, the specifics of Smith's personality and circumstances are hard to separate from the movement he spawned.
Probably the only two individuals on the list whose impact on US history might be considered irreproducible are Smith and to perhaps a lesser extent, Young because creating enduring spiritual systems [Mormonism] and political states [Utah] seems more dependent on individual characteristics than the roles filled by other individuals.