We've no idea Strat. We never do, that's the problem.
For a real question, what would have happened if the Spanish/Portugese hadn't pissed all over South America. Then stamped some more. Then started being really nasty to the place.
You could argue that stopping the Atzecs was probably a good thing, I have never been a big fan of tens of thousands of people being sacrificed alive to dark gods on a regular basis. However the Inca and many other advanced tribes, aside from a slight Llama obsession, didn't do anything to deserve extinction.