That is pretty rough. I am afraid that it is a little early to tell at this point what the extent of the damage will be. If the leaves drop, that is a good sign, so is green cambium. As long as there is green under the bark above the graft, there is hope. At 26, ice is your friend as long as it keeps forming. There is a whole complicated discussion involving wet bulb and dry bulb temperatures. The layman's summary is that because of evaporative cooling when you first turn the water on, it is safest to start running the water it at 35-36. And then keep it on until the ice has melted off the tree (usually around 40). Following those guidelines will cause the least damage to the tree as long as you have enough water for the wind conditions. More wind requires more water because it causes more evaporation. If it makes you feel any better my Dad lost a door yard citrus grove the same way back in the 80s. He learned his lesson, and we have been very successful growing fruit since then.