I have to say I agree with mmm. I think the idea of Paul and Ringo hanging around until after George's death to finish off Now and Then and release it would be appalling. No matter how they dressed it up, were it to be the case, it would be the first time in their career that they released that one of them (George) had explicitly vetoed.
Though, you could argue the other three did it to Paul with Let It Be. They just didn't let him hear it until it was too late though.