Tom sent me some interesting links just in case you toast e2k7 users by mistake :-| Not tested this yet, but might just for the fun of it in my lab
Undelete the OU/Users/Groups via ADRestore.net (http://blogs.microsoft.co.il/files/folders/guyt/entry12573.aspx)
– or –
ADRestore v1.1 (http://technet.microsoft.com/en-us/sysinternals/bb963906.aspx & http://support.microsoft.com/?kbid=840001)
Then reset password, enable account and re-attach the mailbox.