Thanks to all, a lot of interesting and funny comments.

majorwibi, here's an update to the rest of the story. After an earlier post I emailed Delta to find out specifically:

"Hi, I've copied the below from the SWU located in my profile. I'm interested in learning what the current priority rules are regarding filling empty seats in BE on international flights when Z class is not available? Specifically, if I meet all the criteria for an upgrade to BE, Y,B,M coach fare; use miles or SWU to upgrade, will a non-revenue passenger have priority? I realize Delta may have operational requirements to move certain employees to prescribed locations and understand this may be an operational priority but what about others?
Thanks.
v/r
Delta First"

Dear DeltaFirst,

Thank you for your e-mail to Delta Air Lines.

Being a Diamond Medallion and meeting all the criteria mentioned sounds excellent. Revenue passengers always have priority over nonrevenue passengers.
(At least they are supposed to.)

DeltaFirst, thank you again for giving us an opportunity to respond to your concern. We very much appreciate your Diamond Medallion loyalty to Delta and look forward to the privilege of serving you again soon.

Sincerely,

Ginger James
Medallion Desk
www.delta.com