Replacing birch on just one wall

If you are looking at replacing one whole wall, along with vikx's good advice please be aware that moisture that intrudes under the skin does not respect the laws of gravity, by flowing straight down the wall from the point of entry. It has a tendency to migrate along framing too. It may be, that while most of the moisture has run down the one wall, that the corners to at least midway on both end walls as well as along the ceiling framing my also have had smaller amounts of the moisture migrate and start it's deterioration, but not yet to the point of panel warp/frame rot/sag. Lift the skins front and back too, and make sure you have the whole problem identified, and give the ceiling panels some attention to signs of staining/discoloration or the beginnings or sag closest to the damaged wall.