If KE stranded you at another airport and you had to buy a most likely full fare one way coach ticket, that would be easily sueable in court. KE knows about this fare, and assuming they do not have retards in their legal office, they are probably going to honor this as the longer they do not the most it would cost them. They got about 500-600 out of a lot posters, if they not honored the fare, at the very least they will lose it, possibly go with an empty seat (if denied at the gate), be possibly on the hook for hotel and excursion cancellation costs (if not the cost of a full hotel stay as some hotels offer the best price if non refundable pay up front). So instead of taking their $550 in the bag already, KE could not honor but instead of being $550 ahead, could cost them a couple thousand per person.
While companies have been known to do dumb stuff in the past that really burned them in court, I would hope KE would know better.
And remember, mistake fares are not for the risk averse faint of heart traveler, things sometimes go bad with these arrangements.

Finally, if we get to October and this is still showing, I think we got this one in the bag.