BA cleverly picked the "end of timetable" date for ending the KJ tie-in, which makes life much simpler. Not sure that there is much danger of flights being dropped individually prior to the end of the agreement (BD seems to indicate that it will initially operate all the routes in exactly the same way as before, and the airline was profitable so no hint of cost cutting). Any open-dated tickets wouldn't be able to book a "post-breakup" date, unless an agent makes a mistake (which I suppose has been known to happen).