If the lens coating is torn or worn of by extended use, is it possible to reapply it? I don't mean a do it yourself repair, but rather a repair performed by the manufacturer. It also may very well not be cheap, I realise that. Are there possibly some optical properties of the lens that are so delicate that they render a repair like this impossible?
Most likely not. The lens coating would have to be removed before it could be reapplied in most, if not all cases and that would likely end up deforming the lens itself. You could always completely replace the element if it is sufficiently damaged to be a problem, but it is unlikely that minor issues with the coating are going to cause significant issues.
I've had scratched anti-reflective coatings on eyeglass lenses removed in the past. Since the coating had been on the lenses for a few months it did not all come off but left a slight tint over the entire lenses. I chose not to have them re-coated because I figured I would also scratch the new coatings.
It would probably be more economical to replace the front element of the lens than to have the original coating removed and then reapplied. And since the manufacturer would likely not even consider doing such a repair, you would probably have to find a third party lab to do the work.
Whether that would be more economical that just replacing the entire lens would depend to a great extent on the value of the lens in question. It would probably cost more to have a sub $500 lens repaired with a new front element than it would cost to find another used copy for purchase. On the other hand, with a $1,000+ lens it would likely be cheaper to replace the front element.