Metal Limbs.

[Hawk]

This thread covers nicely Troll regen:

viewtopic.php?f=78&t=395

[Arrillion]

Trolls are like skinks, they can regenerate limbs because stemcells still have the memory of the lost limb in their DNA.

Actually Humans can do this thing too, although only with finger and toe tips and in most cases only when they are young. The liver can regenerate from as little as 25% of it's tissue. So humans have the inert ability to regrow limbs.

Some interesting information about regeneration.
http://en.wikipedia.org/wiki/Regeneration_(biology)

The wiki states that the complexity of the animal, and thus the limb are key to it's regeneration, as such a Troll might not be able to regenerate an eye, but would be able to regrow a leg or an arm.

About mechanical limbs, I think it's possible, but there are a few things that should be taken into consideration.

1. A mechanical arm wil never be as good as a normal one, especially when it comes to moves that require precision, such as grabbing a glass without breaking it. The arm could also not be able to move in every direction.
2. Using a prosthetic limb would take weeks if not months to master completely.
3. Like any piece of WoW engineering, they are prone to malfunction.

About healing limbs from scratch, I think only an epic priest would be able to carry out such complex procedures. Reattaching the lost limb wil make the procedure a lot easier, but still hard to accomplish.

Ressurection are matters of spirit, and should be left to Trolls and other shamans. But that's solely based on my opinion.

[Vorce]

Limbs could in fact be reattached, under certain conditions (For more information, check out Magic and You - Understanding the Mystical under the 'healing' section) ^^ They most probably won't be able to 'regrow', unless its some small limb as elaborated by Arrillion. As for prosthetic limbs in WoW, don't forget that we have magic, and while it can't do everything, I think attaching a metallic arm / leg and enchanting it to have it connected to the user's nervous system isn't that far fetched. However, maintenance would be the key issue when it comes to metallic limbs, assuming that you manage to find engineers to create the limb, surgeons to attach it and magi to enchant it. The picture painted by bounty earlier fits the bill, because obviously, it won't be able to function as a normal limb. It would always be a problem, in a good way =) haha