Thanks for all your answers. I didn't know about ORC but the combination SK A3 seems to be complicated to get credited. As I understand I'd have to contact SK to credit the original routing to A3.
What I was wondering when you get rebooked on another airline would they book me in a return fare booking class or a one-way on the new airline. Usually the one-way fare classes are the higher ones as they are more expensive. The SK booking is a return fare but would they adjust the booking with a new outbound flight on another airline or create a new booking with a one-way flight.