I'm very sorry that your Raz has been attacked with such severity.
Plucking the feathers on the neck/head area is considered a vicious act and when measures aren't taken to separate the budgies, this plucking can and will progress into vicious biting on the head/face areas where the eyes, cere/beak are included.
At the first signs of feather plucking, immediate and permanent separation should have been implemented.
There are no excuses for this kind of aggressive behaviour and your Nemo should be housed solo in a cage indefinitely.
I would not recommend a cage with a divider. Most if not all dividers are barred just like the cages and this hardly offers protection if the bullied budgie happens to stand on the divider, a budgie can still be attacked on the feet, beak and get feathers plucked.
It's best to get a new cage for Nemo and when Raz is completely healed and the tempers are more settled, later on you can place both cages on the same room and see how they go about it, if Raz seems stressed, then you can keep Nemo on a separate room.
It's best to keep a safe distance between the cages, again to prevent them from getting close enough that an attack can happen.
I'm wishing your Raz a steady and full recovery.