If John's "long weekend" with May Pang had ended differently, there might very well have been a Beatles Reunion.
John and May Pang were due to meet up with Paul in LA, where Paul was recording Venus and Mars. This never happened because the very week that they were due to meet up, John went back to Yoko.
John had already jammed with Paul in March 1974, in a session released as the bootleg album, A Toot and a Snore in '74.
If John had stayed with May Pang and met up with Paul for the Venus and Mars sessions, John would have probably played on Paul's album. All of the individual Beatles played on each others solo projects. With this last combination of John playing with Paul - this would have been the most likely spark for a Beatles reunion. We'll never know...
Lots more on my website..: Rock'n'Roll Unravelled - the story of rock'n'roll from its roots to mid-1970s punk.
Author of Rock'n'Roll Unravelled, Derek Shelmerdine - fortnightly guest appearances on the Mop Tops and The King radio show; with his segments, The Beatles Unravelled and Elvis Presley Unravelled.