Its probably trashed as the electrolyte has snuk everywhere if the corrosion is that bad!
However, you can try a rescue even with the odds against you.
The electrolyte is usually alkaline in nature so a mild acid will neutralize it, but at the risk of doing additional damage. Be prepared to neutralize the acid after it has neutralized the alkaline using something like baking soda & a distilled water rinse follwed by complete disassembly & drying.
Try mechanical means such as picks & needle nose pliers to remove the corroded in batteries first & be prepared to be dissapointed.
Allan Quatermain: “Automatic rifles. Who in God's name has automatic rifles”?
Elderly Hunter: “That's dashed unsporting. Probably Belgium.”