I'm not sure I've ever heard of anyone having them relocated. I think there'd be multiple concerns: removing them from their blood supply, re-establishing the blood supply in the new position, and repairing the cosmetics of the site they were removed from.
BUT, those are all the same concerns that come up in the initial procedure as well. And in the case of nipple death, I'm sure they do something to remove the failed graft so that you can pursue medical tattooing.
It doesn't hurt to ask your surgeon and get a second opinion from another surgeon. Worst answer you'll get is no. I'd be surprised if it absolutely could not be done.