However, other steps to consider (having been there, done that):
* If you were using Sync Services with v11.2.3 and you had made a backup
of your contacts in Apple Address Book (there's a menu command for it
there), you could re-import that backup.
* If you are on an Exchange server, and your admin has backups and
supports restoring accounts (possibly to a .PST file, requiring
Outlook/Win), you could get them from that.
* If you sync to a Palm device, you could at least get some of the data
back from that.
* If you'd used the Database Utility to make a copy of your Main Identity
at some point, you could get contacts that were part of that Main Identity.
* If you had copied any contacts between folders in Entourage (such as
local to Exchange, or vice versa), you could use those copies and restore
from them.
* If you had any copy of Entourage or Outlook accessing the same Exchange
account (if it was Exchange) and had not yet connected to that account from
that client after deleting the contacts, you could make sure the client is
off-line (so it doesn't sync to the address book with no contacts) and get
the contacts from it. Careful, though!
This may not help now, but at least may give some ideas for future backups.