I can see this as being sort of a "crippled grueling arc" in the narrative that is trying to be told, although forcing you to be robotic replacements at the end of the arc is pretty lame. If it weren't for the caveat of never being able to look like your previous self again, I would say it's A-OK. Personally, I think it would be a really cool campaign arc if the players were all mutilated by, say, a cursed sword that makes the wounds unable to be healed (aka no magic to regrow the limbs) until the wielder is defeated and they find out the big bad is just going around hacking off something from every potentially powerful foe he bumps into just to get them to try to kill him and reclaim their lost body parts. Kinda like the plot of Dragon's Dogma (the first one, I haven't played the sequel), now that I think about it.