Hello, Last spring (2012), I thought this one was a goner, like others that didn't survive the weird winter we had in 2011-12, but I wanted to save it. I removed the dead bark until I found some "green" (cambium) with a clean sharp knife, applied copper sulphate (Bordeaux mix) diluted with water to make a kind of paint-like paste, applied it to the wound, let it dry for a couple of days, then put some wound-sealing paste I use for my bonsai. And apparently it worked. After one season, the tree has developped a nice, healthy scar. New buds have even appeared on growth rings that stayed dormant for years. Now, I'm planning to "refresh" the scar when it's active (April-May). See the photo with a lght green line. Another solution would be to carve and treat the dead wood, and then make a "bridge-thread" graft. Healing would be even faster, but it would require the same variety as the rootstock to be "elegant", otherwise it might bulge, or on the contrary be weak, or lead the way to other problems.