There will definitely be some volume loss after the HA fillers are reabsorbed, but you will not be left worse off than prior to the HA filler injection. This is because besides volume replacement, HA fillers stimulate collagen production as well.
This also helps with some volume replacement, as well as improving sagginess and skin texture. Hence even when the HA fillers are reabsorbed, you will return to a skin age/stage which is better, compared to if you had no fillers done.