I think it is unlikely we'll be able to keep our WP# or even some variarion with a prefix.

Why? DL seems to be on a tear to replace anything NW related -- an example: I was in the LAX WC the other day and the NW coffee mugs where replaced by Delta ones. Normal prodedure you say -- but the WC will be closing at the end of the month with the move to T5 but they still took the opportunty to get the NW logo out of sight.