In reply to tlm:
There's a fair argument that after such major trauma the injured person would no longer be the same person you entered the relationship with. In one sense they obviously are, in another they are fundamentally changed.
Along similar lines as Theseus's paradox, while we all change physically over our lifespans such a sudden change fundamentally alters the identity of the person you entered in to the relationship with. Even over a period of time, substantial changes in personality and physical form are, in my mind, grounds for separation. If my other half became a slug on the couch, surrounded by pizza boxes, watching only day-time TV, I'd feel justified in no longer holding a life-long connection.
When taking up paragliding I told my fiancee that, should I suffer a severe spinal injury, I would hold no grudge if she left me to spend her life with an able-bodied person. Even if it resulted from something unrelated to this or climbing, it seems to me to be unfair to expect someone to have to alter the rest of their lives to service my disability.
It is a slippery slope though. What about disabled children? Caring for the elderly, etc etc. Ultimately its down to the individual and, like abortion, I don't think it is right for anyone outside of that relationship to stand in judgement over the choices made by those in the relationship.