Sorry about your chicken. I had four elderly hens living here, and they got sick eventually.
My mum kept chickens too. In my experience they don't have much of a fighting for life instinct and die quite soon when their time is close. If he isn't in pain, I'd just nuture him. My mum kept an old hen who couldn't walk for a year before she faded away. That hen enjoyed that last year, she was hand fed, cuddled and had water brought to her beak three times a day. I took to calling her Queen Victoria.
We took one hen to the vet and had a medical inspection of her and medicine, the experience freaked her out and she still died.
Both me and my husband have euthanathiaised- killed- birds here. There is no way to make it beautiful. One way is to break their necks, which is harder than it sounds unless you've done it dozens of times, the other is with a cleaver. I don't recommend it unless they are in agony. I think chickens can rally if they are encouraged, or die quickly if they are ready to.
My greatgran used to slip one drop of brandy down the throat of any ailing hens and it often revived them. My mum fed hers cobwebs as they are antiseptic( or a similar word that I've forgotten, but that's been confirmed to me by a hospital doctor).
What do they do (if anything) on the chicken farm? Could you ask your father?
Best wishes for the chicken whatever happens.