I thought of 2 ways that you might implement repairing..1. You just can heal. Whenever you get a limb lopped off, you spend energy to regenerate voxels slowly to heal it. Now, you won't die from losing any limbs, but if your head gets hit while limping around and waiting for your leg or weapon arm to come back, that's it .You would have no control over when you are using the energy, so its a bit less over-powered.you spend energy to get it back
2. Healing would be and upgrade. Same as the first, you won't die from losing limbs and it takes energy.
I like 2. better. Which would you prefer?