Here's a question for alternative universe ponderers. Ringo quits during the White Album. Only in this universe he never comes back. Pauls does the drumming until a replacement is found. Who is it? I don't know--haven't figure that out yet.
George also quits, feeling slighted by the lack of input of his songs.
John talks a distracted Eric Clapton into subbing for a band now called the Lennon & McCartney Experience. Or the Lenna-Macca-Expa, for short.
John and Paul are able to pursue side projects: John does his Heavy Breathing released in 1969 and Paul offers the public Granny Pinched Me on My Arse the following year.
Meanwhile, Ringo starts a two-drummer band with erstwhile Beatle Pete Best. While their recording success is limited, they becomes an opening act for Elvis in Vegas. Ringo is reported to say, "El was always bigger than the Beatles."
George, meanwhile, takes up ostrich-farming as means to offer the world a low-fat white meat that tastes as good as chicken. Although this endeavor fails, he does popularize the sport of ostrich-polo (particularly in South Africa). He continues to dabble in music releasing a solo album every ten to fifteen years.
Lenna-Macca-Expa finally disbands in the late-70s as a disco album bombs. Macca, however, has been saving all his money and buys the Beatles catalogue out from under an outraged Lennon. McCartney then goes back and rerecords every album in the Beatles catalogue--with McCartney playing every instrument and singing every part. This keeps him busy through the mid-90s--preventing him from recording a lot of crap.
Lennon finds happiness, not in the arms of Yoko Ono, but making and flying ultralight airplanes. He designs his own fourteen-winged plane out of tissue paper and balsa wood and tries to regain fame in 1980 by making the first transatlantic solo flight in an ultralight aircraft. He takes off from Long Island, but abruptly crashes on Montauk Point, putting an end to "the dream" forever.