The big disadvantage the Beatles had is that each member was so well known. You get some groups from the 40s, 50s, 60s, 70s, and no one really knows their names, or the average person doesn't. Like Herman's Hermits, the Dave Clark Five, the Platters, and so on. For groups in that category it doesn't matter if they're alive or dead, someone can own the name and go out on the road.
I've seen the Diamonds a couple times, and I think they have some relation to the actual group that recorded once upon a time. But when it comes to these Diamonds there might be a few carats missing. Who knows? They know, but what do I know? I never knew their names anyway.
The Monkees, basically everyone who knew anything about them knew their names. So you couldn't have Mike, Rick, Tim, and Fred as the Monkees and fool a lot of people.
Of course the Beatles are in that category. Even though there were other Beatles -- Pete Best is the one that comes to mind (Stu Sutcliffe, but he died a long time ago) -- there are only four Beatles that have or can have any relation to the group that we've all known and loved. And we know those four individuals intimately.
Paul and Ringo recently reunited for an event, something about raising money for Transcendental Meditation, it sounds like. They did some Beatles' songs, but there's no way they could get two other guys and call it the Beatles.
Anyway, nice to see they're still around!