In case of invol. cancellation you can rebook your Avios ticket to any dates until Dec 2021 - award availability does not need to present, i.e. you have a very flexible ticket.

If active segments remains in your reservation, you need to contact BA before the first of those flight dates to have these segments removed from the reservation (otherwise you will no-show for these flights).

There is plenty of information in other threads in the BA forum about invol. cancellation of Avios tickets due to Covid-19.