To be fair, that route is insanity. Zeds already cover a lot of uncomfortable situations (I worked with disabled people, and Zeds are often rather misappropriated in like or form, which would give real life people unfair treatment for being “strange”).
So just be careful how you treat it, for your own sanity.
The game world has replacement organs to some extent with CMBs, though it would be very expensive and/or need to be found and not crafted post cataclysm. The possibility of organ transplant (and cloning) seems there too in the game lore (vats exist in labs).
So fully curing someone who has not been injured/infected past recovery seems possible if treated quickly enough. But for a full on Zed? Seems their organs and brain are goo already.
Could start simple. Give an NPC “find antiserum/cure” mission. And then make some sort of cure to find in a lab. From there, the NPC could need many other types of treatments.