Don't know about elderberries, but I've had a similar experience with shining sumac: rapid and seemingly catastrophic wilting no matter what. The first time I just abandoned the plants, but to my surprise a few months later new growth pushed through the soil. It was a bad spot for them, so I moved them to a raised bed, with the same result: total failure of the current growth, resprouting from the roots. Not only that, but I'd apparently left a little root behind, because I got more sprouts from the original site. When I finally decided on a permanent home, I moved them from the raised bed during the winter (no active growth); they were slow to sprout, but are doing fine, and guess what? I've got new sprouts from both of the original temporary sites! I've also had this happen with sycamore and parsley hawthorn.