Well, we can see the example of the Arabian Peninsula under the sahaba . There were no polytheistic idolators found on the peninsula from their time until globalization began in the 20th century. Similarly, in Africa, you don't see many (if any) animists in northern Africa. It isn't really a speculation - speculating about the past is almost always pointless if there is nothing to be learned - but it should act as something to remind ourselves as we move onwards to the future.