If you think you've got the water stopped, I'd try to let it dry out. A fan blowing a a low speed, would move some air and help the process. Once it's dry, which will probably take a couple weeks, the wallpaper may shrink down and look pretty good. If it doesn't, you'll have to find a way to get some glue behind it. I'm guessing you can't get at an edge to peel it back, so you may have to cut it to allow a way to work glue in. Probably something like wallpaper paste would be the best, because you could work it around, then wash off the excess.