I am sure that if the Beatles hadn`t broken up, they would have been a great band in the 70s as well, considering their Abbey Road, which was quite unlike the previous ones and their wonderful ability to keep up with the times and new ideas. I even think they might have become more rock and still have those beautiful love songs.
"Words are flowing out like endless rain into a paper cup, They slither while they pass, they slip away across the universe. Pools of sorrow waves of joy are drifting through my opened mind, Possessing and caressing me." "About a lucky man who made the grade" "I'm coming down fast but I'm miles above you."
Can you imagine if the Beatles tried to get into Prog-rock. or disco? It just wouldn't be the same. Or what if they continued into the eighties and did new wave and synth rock? I shudder to think of it.
You're so vain, you probably think this post is about you.
Well John and Paul did have a brief reunion in the 70s - google 'a toot and a snore in 74' for more info on that.
Incidentally, you should check out this album: Chris Singleton, Twisted City - http://www.singletonmusic.com/freealbum. It's been released as a free download and is very Beatley. I think it's a bit like what the Beatles would sound like today.