i just opened \home\user\.osso-abook-backup\.osso-abook\db\addressbook.db with a text editor on my pc, manually copy/pasted all the data back to my n900 contacts through vnc (x11vnc package on n900, tight vnc viewer on desktop). kept me busy for over an hour. of course you can paste your data in nokia suite as well and upload that to the n900.

made backups and exported them as vcards straight after, so it won't happen to me again.