Great idea for a thread!
I'm closest with Fendertele on this one. Paul and John were a songwriting team; I don't think either would have developed without the other. They relied on each other, encouraged and spurred each other on. If you take apart that early partnership, started at age 15-17, I don't think Paul would have done diddly in music. He would have done what his dad wanted, and become a teacher. He was the first to quit the band after their first Hamburg gig, and John and George had to lure him back away from the dockyards. Paul=absolute no. Nothing to do with talent, but he needed the Beatles, and John in particular, to get going.
John needed a gang. He said so himself, and I believe him. He always wanted to be part of a group, and to be famous-- but without the group, and the right group, I think he would have ended up in jail like he thought. He was one of those people who could never have fit into normal society. Tragic, but I think that would have been his path.
George never wanted to be famous, but he was a damned determined musician. I can see him being a musician all his life, a sideman for some band or a lot of bands. I don't see him in the limelight, but I see him pursuing his dream. He was the steadiest of the early Beatles in terms of always playing gigs. I doubt he would have written his own songs without John and Paul as an example.
I think Ringo would have enjoyed a few years as a drummer, maybe kept it up on the side. But he was a family man-- adored his family. I think he would have done whatever he could to support them. If drumming didn't pay enough, he'd switch to another job, and just drum for fun.