Yoko once said something interesting in an interview about John’s Lost Weekend, when he and Yoko were separated and John was living out in L.A. During that year and a half separation, John was hanging out with Keith Moon, Harry Nilsson, and partying a lot.
Even Ringo and Paul came out to see him during that time. John was very unhappy, drinking too much. He would enlist friends to call Yoko and tell her how much he missed her and how he was ready to come back to her. “I told these people”Yoko recalled. “You all said I was keeping John from you! Well, here he is! You take care of him!” So it seems to me that when John was in LA in that ’73-’74 period, there was nothing stopping him from working with Paul again.
Paul even visited John for a few days, and they apparently had a warm visit, and jammed together (the recording, “A Toot and a Snore in ’74”) is available but unfortunately there are about 30 other musicians on the recording, all drunk and high, so it’s very poor quality). Anyway, John had a chance to work with Paul again, but didn’t take advantage of that opportunity. Maybe they just weren’t ready at that point (and Paul was busy with his Wings over America tour). Here is a photo of John and Paul in 1974 in LA).