What if The Beatles never existed?

The absence of The Beatles is hard to gauge, because they have influenced pop culture and society in so many ways. Very few artists/bands have single-handedly changed the face of music to the extent that The Beatles have.

This is a controversial opinion, but I have my doubts that the British Invasion would ever have occurred in America. The Beatles opened the floodgates for other British artists to achieve success, yet I don't think The Beatles could easily have been replaced by another band. In such a scenario, bands such as The Rolling Stones, The Who and The Animals still would have found success in the UK. However, I doubt their success would have transcended into other countries around the world, at least not to the same extent.

Surf rock likely would have become the dominant genre of rock in the US. The thing is, even though The Beatles were the dominant act of the time, The Beach Boys were significant and influential in their own right. They essentially did lead the surf rock movement,so the absence of The Beatles likely would have propelled them as the faces of rock music.

I think Hard Rock and Heavy Metal would have likely come to fruition, even with the absence of The Beatles, due to the experimental nature of the Late '60s counterculture. Nevertheless, the two genres likely would have emerged around the same time period. 

There's a strong possibility that Motown would have been more influential throughout the Mid-Late '60s. However, it likely wouldn't have lasted any longer than it did. I think it was inevitable that rock 'n roll would become the dominant genre in music. It wasn't a matter of if, but when. As for Disco, I personally don't think it would have changed all too much, had The Beatles not existed. Disco itself was an underground movement in Europe during the Late '60s/Early '70s and I believe it would have had the same trajectory/influence in the mainstream.

The last question is a bit more difficult, because there's no real way of knowing how rock/pop music would have panned out. I think Mid '60s music generally would have been more conservative in America, in such a scenario.