I'm in exactly the same situation. Got all screws out except the top-right silver one which wouldn't budge and is now stripped. Put the phone back together without 4 screws and the retaining clip thing and it's working fine! So until I can borrow a mini dremel type thing and extract/kill the offending screw (and probably break the phone at the same time) I'm still with a black case, but I shouldn't to worry about a missing screw afterwards - we'll have just upgraded to a very slightly lighter version of the standard n9!