Hello
Just as a data point…
F>J downgrade, badged as cancelled in the booking.
Outbound was paid F, inbound was UUA to F.
Options, once the agent spoke to a supervisor, of full refund, fare difference or compensation.
I accepted the compensation on the outbound (£425 each vs £225 fare difference) and a refund of the Avios on the inbound. Seemed very reasonable indeed.
There was an outstanding balance and the £850 was knocked off that.
Hope that helps someone,
TFC