How to cancel or claim a facebook page

I would try him first, if there is any way at all that you can get this information out of him. If that is impossible you might (I'm not sure about this) be able to appeal to Facebook, but the bottom line is, FB has few people on its Help Desk staff and they are FAR more likely to help big celebs. As in, "Let me help you with your account, Mr. McCartney."

Barring that, try guessing the password and, if that doesn't work, create a new page or group, make it clear that you are abandoning the old one and do just that - and make sure 2 or 3 people have Admin status so this doesn't happen a second time.