I am in exactly the same position, original flights booked in 50% Avios sale.
LAX in F returning from Charleston for April ‘21 (route suspended and changed to Atlanta) was only allowed to change flights to OCT ‘21 - typically both these flights are still flying with no sign of any cancellations or re scheduling - LAX flight this Sunday 3rd !!
I have held out until now hoping for a change to my flights enabling me to change dates to November but doesn’t look like it’s going happen, so now only option is an FTV (241 voucher also used and only valid until Jan so will extend the life of this) but virtually no chance of rebooking these (or similar) flights even using full Avios as no availability to most of USA.

So would be very interested in the outcome of the OP case ………