Alright, here's an AH challenge that might be a bit ASB, but let's see if it can't be done.
Your mission, should you choose to accept it, is to have the Beatles not break up when they did. All four members must stay in the band until at least the 1980s, so no replacements. Bonus points if you keep all four of them (and this would require butterflying away George's and John's deaths) still active as a band to this very day.