I attended a recent lecture given by a member of the Bentley Priory Battle of Britain Trust. The plan is to sell the site for conversion into luxury flats with a clause that important parts must be refurbished and kept open to the public. A deal was put together last year but on the very day of signing the company put in a lower bid and so the whole thing fell through. As far as I know the MoD are still looking for a new developer.
Rest assured, the trust have infuential people on their side and are determined that the history there will not be forgotten.