As we see here, in Star-Wars, cybernetics is preferred over cloning to replace a lost limb.
But what if the clone is already there? In the particular case of Clone Troopers is there any mention anywhere in EU that the organs of dead Clone Troopers are kept in a organ bank for future transplantation?
Two novels in the Star Wars expanded universe offer a lot of insight into clone trooper medical care: MedStar I: Battle Surgeons & MedStar II: Jedi Healer (2004) both written by Michael Reaves and Steve Perry. The books focus on Republic Mobile Surgical Units (RMSU) - (pronounced "rimsoos") on the front lines of the Clone Wars. Think of the RMSU's as Star Wars MASH units.
To answer your question, YES, doctors used organs and body parts of dead troopers to patch up wounded troopers. They also had a supply of freshly cloned organs to use.
And if you want more insight into life as a clone, check out the Republic Commando series of novels written by Karen Traviss:
Republic Commando: Hard Contact
Republic Commando: Triple Zero
Republic Commando: True Colors
Republic Commando: Order 66
Imperial Commando: 501st
In Republic Commando: True Colors, there's even a part where an injured clone is brain dead, but he's rescued from the hospital because if he's not fit to fight, then his body is just recycled back into stock. So basically, you only medically treat clones so much before they "total" the clone and put his parts to use for other clones who can be saved.
I think there's an implied double-question here:
And, as shown above, the answer to the 2nd is "No." It's not cost effective for them to do that. While some Jedi show compassion for clones, some don't, and in terms of cost, speed, and battle-readiness, this is impractical.
But as a direct answer, yes, they could be used as a replacement, since they match genetically, have the same blood type, and so on. We can do it with our tech, so there would be no reason they couldn't do it. (I suspect most of the time there's no real reason, since clones are cannon fodder, but they might find it worthwhile if it were an extremely experienced commander who's life could be saved.)
I tried searching the Wookieepedia for anything about clones and transplants. The only reference I found was that cloning was expensive and outlawed after the Clone Wars, leading to the use of cybernetics instead of cloning. (But that doesn't provide an instance of transplants for clone troopers.) (I searched using Google and the Wookieepedia search functions for combinations of the words clone and transplant, as well as a few others like replacement, organ, and limb.)
While I can't cite an example of this having been done, I can't find any examples of it anywhere in the Wookieepedia.
As far as canon tells us, clone troopers are meat for the grist mill, and easily replaced. Most of them don't even have names; Commander Cody is a rarity likely afforded by his relatively high rank.
As such, I wouldn't think the Republic/Empire would care much about keeping the clone troops alive. If you can survive and be combat-effective without a particular organ or limb, great, otherwise you're pretty much left on the battlefield for dead. Even a cybernetic limb would only be an option to the more valuable clones that had demonstrated enough individuality and combat effectiveness to be promoted to non-com.
Remember, the clones were intended to fight droids, and so human compassion is a weakness that has absolutely no place in a clone's mind. As such, first aid is limited to patching holes in cases where the clone can remain effective if you just stop the bleeding. The Republic might well order clones that survive a career-ending injury executed.
