I'm not a mental health professional, but I am an attorney. And any attorney who has some experience practicing criminal law, builds up at least a little subject-matter knowledge on the drug/crazy connection. If there are some therapists reading this, perhaps they add some actual expertise, but....
I think there is a nexus between some drug use (meth especially) and bipolar disorder, and that connection goes both ways - sometimes the bipolar disorder is the rootcause of the meth addiction, and other times the meth has so damaged the neural pathways, bipolar disorder (and other mental illnesses) is the end result of the meth use. IOW, just stopping the meth use won't necessarily "cure" what's ailing the addict. The damage well indeed be permanent, and have to be managed for the remainder of the addict's life.
I am not the expert you were looking for but I wonder the same thing. Bi-polar disorder is not a disease that can be positively tested for it is a cluster of psychological symptoms. There is no doubt that drugs like cocaine, methamphetamine and even alcohol can bring on psychological issues by altering brain chemistry as well as exacerbate existing problems.