If you do get a change, save your original ticket and your boarding passes and claim for original routing credit when you get back. Unfortunately this may take a very long time to come through - I’m still waiting for ORC on my flight home from Japan on Feb this year where the connection SYD-CBR was downgraded from J to Discount Y causing a loss of 30 SC, plus another 30 SC owed because it was a double SC flight booking. You will have to be firm with them, but when the downgrade/reroute is involuntary, you are entitled to the SC originally booked if that’s better than what you end up flying. Be persistent and patient.