I doubt a reunion would have challenged the heights they achieved in the 60s. But I think it would have easily surpassed most of their solo stuff.
I guess the question is, if they had, where would have it ended. Would have they dragged on into the 80s ( assuming in this alternate history John remained unassassinated) I'm glad that they didn't peter out like so many bands. They had a definined endpoint and, except for the Threetles stuff in the 90s, left their legacy as it was.
That all said I'm sure an album or two in the 70s with the pick of their solo songs getting the Beatles treatment would have been a good listen.