It'll probably be similar to how Europa Universalis 4(Paradox's latest game If you don't know) has a mode to turn on historically lucky nations. It helps it play on a more historical role so England, Spain, France etc all have a better chance of surviving and thriving like they did in the age of expansion.
Playing historical mode will probably assure that things like Poland marching on Berlin, France blitzing through central Europe, or Stalingrad falling in a week don't happen as often (although its never 100 percent). It'll also ensure that the ai nations choose historical techs. Playing ahistorical may have Germany focus on a Grand Fleet and successfully invade the British Isles, Soviets developing ICBM's, or even a war where instead of axis vs allies and Comintern it could be axis and Comintern vs allies, or another country such a spain, japan, or France making a 4th, 5th, and or 6th faction. Central and southern America could even join a new faction to try and cut America down to size, while being led by Japan(that actually sounds like an amazing idea).
Basically, the game is only about 12 years(although can go on for 1000 if you so desire), so in that space only so much ahistorical mumbo jumbo can occur, but yes, if you do a timelapse with all ai controlled nations 10 times, it'll be a vastly different finish every time.
Check out the dev diaries for individual nations and in the tech tree pictures you can see all the different paths a country can take.
