It appears that all F booking is closed from Sep 1st, 2019. Asiana is evaluating various cost reduction measures (including ORD cut) and evaluating-F might be part of the effort. Asiana cannot remove A380 because it's not leased and we know A380 isn't popular at the secondhand market. My bet is to convert F section into economy class. As an interim, those seats might be sold as a premium business class that it does on the regional (HKG BKK) A380 routes.
In the meantime, all we can do is patiently wait for the announcement.. or pray F come back.