that looks pretty severe, i dont think it will grow back. if you are going to euthanise then do it quickly by clove oil or some other speedy method.
please dont put the little guy through anymore pain and suffering by feeding him to your oscar.
If he survives, then he'll never be able to live with other aggressive fish because he won't be able to swim efficiently enough. They might sense his weakness and he'd become a target.
i will take him, why would u kill him. just give him a couple of months to recover, and your not satisfied. well then just donate him to someone who would want him. I will take him, if u lived near by.