I'll throw one on the table with these points on ethics:

Purely hypothetically, of course....

It is also possible in some cases, particularly with new museums or
museums being renovated or otherwise revamped, that a director can
manipulate an inexperienced Board or stack it with old friends, isn't
it?  However, I suppose as long as the Board and the director are happy,
it doesn't matter how the rest of the staff is doing, right? (or how the
collection is being cared for, or how successful the exhibitions are...)

I think the kind of regular review of a director by the staff that Julia
Moore has suggested is an excellent idea.  The worst that can happen is
that everybody knows where they stand and can make informed decisions.
It reminds me of the process they used when I was in college to review
professors - student surveys were a factor.

(As for donors or there relatives getting something back - I say no way.
You certainly can't get back anything you give to a charity, or that you
sell.  "I decided I want my car back!" wouldn't get you very far...)