I believe that Demi will recover...eventually. It may be a long, hard road though. Coke is one of the hardest drugs to kick becaus of the euphoric recall. Your memory basically lies to you and reminds you only of the good and skips right on over the bad. This makes it hard to find reasons enough not to relapse.
She also has mental issues. I believe with good, longtime therapy, she will be victorious in that department too. She will have to work hard though and be devoted and serious about it all. It will have to be the thing she wants most in the world, even over her acting career. I belive that by the time she is forty, she will have her act together. Until then, it may be touch and go.