I had a blind cockerel as a result of an attack by another cockerel. OH dispatched the other cockerel as it had also attacked a hen. The one we kept wasn't blind at first, his sight deteriorated after the attack. He stayed with the hens until his sight had completely gone, then only stayed with them at night, during the day he had an enclosure. Eventually he was showing signs of mental deterioration too as he kept shaking his head and was finding it difficult to find his feed bowl, so we had to have him put to sleep. Yes, at the vets, soft I know, but we had become so attached to him that we couldn't bear to do it ourselves.
I am also of the opinion that if they have some quality of life, why get rid? If the blind hen is laying occasional eggs, and seems happy enough, then leave her be.