Something I’ve seen mocked up by AggeIw (https://aggeiw.deviantart.com/art/Give-me-a-Hand-216238791)
It also begs to reason why Vader would even scream over his mechanical arm getting severed. Maybe there were nerves connected during Vader’s suit construction or something?
3PO feels pain when he’s banged around, burned, ect. And the droids in the stupid torture scene are all screaming in pain. If they feel is somehow, I’m sure Vader does too.
It’s a confused issue for sure. Luke’s prosthetic hand has synthetic nerve endings, but this is presented in contrast to Vader’s robotic suit, which is ‘more machine than man’. If he does indeed have feeling in his robotic limbs, it would humanize him.
It might seem “odd” that he would not react to having a body part chopped off like that to the audience. Also, as mentioned, we see that other machines/droids react to getting hit, cut, chopped, disintrigated … it would be consistent to keep it as is.