As I recall, if you leave a loadable area in which a dead party member is present, the party member is then gone. You could try a PS:T editor, however, and see about editing them back to life from your savegame in which Dak'kon is dead. Mind, I've never tried any of the PS:T editors, so I have no idea how well they work, but they're certainly worth a glance.
This is where you can download them.
As always, back up your savegames before you edit, creating copies in other directories, just in case.
Hope that helps.
EDIT: Oh, and a hint: go back to speak with the NO's old girlfriend. Try different response options, provided they don't insult her. You might like one result you haven't previously tried.