I think my third option (above) is the least ASB..
This may be hijacking the thread somewhat, so feel free to spin it off to a thread of it's own if you want.
What about a POD of April 24, 1976 ?
http://en.wikipedia.org/wiki/Two_of_Us_(TV_film)
As in OTL, Paul & John are hanging out at the Dakota, and they see Lorne Michaels offer $3,000 for a Beatles reunion.
John is keen, but Paul is a bit tired, and adds a convincing arguement.. " anyway, aren't you taking a break from that sort of thing while you bring up your kid? It'll just fire that attention up all over again"
This sways John, but not completely. "OK, tell you what, when the kid's old enough, and I'm keen to get it started again I'll give you a call - It'll be good to blow-out the cobwebs with you when I come back. Do you want to get the other guys in too?"
Paul thinks for a while, then answers "No.. we can always bring them in later - how about just us.. and Yoko and Linda? It can be low-key, fun, no expectations.. and we can just do some crazy stuff again without it being a big BEATLES ALBUM. I have a little studio in England, so we can keep it quiet"
"Sure. If it doesn't work, at least it'll be a holiday." replies Lennon.
I'm thinking if this happens in the spring of 1980, they jam & decide to go a bit nutty and make a "new wave" type album called Darkroom... Basically the edgier halves of McCartney II & Double Fantasy.. Including some of Yoko's songs.