No point moving the booking, because it'll cost more than the flight and I won't be sure when I can fly again, if I can until after the flight.
They don't do refunds on cancellation, but that might let someone else get the flight. However, they make more money.
If I check in online, there's a good chance someone will get an extra seat next to them for 'free' – this feels like the best option.
Or I can do nothing, which I guess may mean they might be able to sell the seat a little earlier if they did have a 'wait list'.