I know it would be impossible for the natives in the north to survive the western powers (bar some horrible disaster discouraging widespread colonization for hundreds of years), but apparently the Spanish, after their conquest of the Aztecs, instituted Nahuatl as New Spain's primary language. It seems that it was only after 1696 that it was banned, so it wasn't just a quick experiment. That's just the language though, and the only real way to keep the natives tolerated is if they convert, but that requires erasure of their native religion. Would the Spanish have trusted the locals enough to put power in their hands? Or does some kind of nationalist revolt have to take place further down the line?