Actually the notification service isn't running/registered but from a user's POV they might just not have a notification widget.
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Service owned by someone else
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The KCM watches the services so the info message updates live if you restart plasma or whatever.
Perhaps I should also make the notification widget aware of the fact that the service isn't registered and then show a crossed out notification icon, or even a "try again" button.
Suggestions on wording welcome, of course.