I wonder if there could be voluntary replacement of a limb with a magical prosthetic, bionic augmentation if you will.
A kingdom with emphasis stumbles upon a higher up in their mortal enemies army. He is abandoned by his troops as he lays, bleeding out on a crimson field following a fierce battle. The general of the kingdom offers the man a choice, join us, and take revenge on those who left you to die, or be sent home in an urn. The man knows his time is nearly out, he cannot afford too many more deaths before his life is over, so he accepts. They bring his dying body to the healers of the land, and as the head healer observes his wounds, he utters. "We can rebuild him. We have the technology. We can make him better than he was." And thus, the first high fantasy cyborg is born.