I think you would be hard pressed to show us a post from the past few years of someone canceling an xONEx mid-trip, without invoking the medical or death in family exception. Yes, the question has been asked many times but there is also little, if any, anecdotal evidence on people canceling xONEx mid-trip and there success or failure. I would venture a guess that the number of posts about people being charged for canceling an xONEx mid-trip correlates pretty well to the number of posts about people canceling a xONEx mid-trip in general. Missing the last "yet to be booked" segment of an open dated paper ticket is one thing, but missing a few remaining flights of a xONEx e-ticket is another. I don't believe I have seen one post on this subject. BTW, did the OP indicate whether this was an electronic or paper ticket?

Note to OP: please let us know how things work out so we will have the start of our anecdotal evidence in regard to xONEx tickets being canceled mid-trip.