Stu Sutcliffe was the original bass player for the Beatles and is sometimes credited with coming up with their name. In 1962, he died an early death (believed to be the result of a head injury from a fight in 1961).
But what if he had lived? Could he have stayed on with the Beatles, or would he have found success as an artist?
He had already left the Beatles in late 1961, so I don't think his survival would've mattered much.
Stu was a notoriously bad bassist, brought along just because he was John's best friend at the time. Whe Stu met Astrid Kircherr in Hamburg, it was all over for him. He stayed there until his death.
For this to have significant impact, either you have to have him not meet Astrid (which butterflies away the haircuts she gave them), or have her reject him maybe, which turns him to is bass in frustration, really learning the instrument. In reality, he probably would've consoled himself with his painting, which he was very good at.
Some were saying he was about to break out as a painter when he died, so his biggest impact could've been there.
If Stu stays with the band in any other fashion, the Beatles never become anything more than a so-so bar band with a weak bassist.