I don't have experience with my AH changing or becoming sober. All that comes to mind re: your question is this: If you have doubt about whether you want a divorce, I'd wait. You can still separate, spend time apart and watch from a distance to see if the BP2 diagnosis and meds really are helping and take your time to decide on a long term plan. I'm really trying in my own life to go with the one day at a time mentality and that includes not making life changing decisions instantly. If you see genuine change in her (and to this outsider her explanation of using alcohol to medicate herself prior to getting proper meds does sound different than an A who craves alcohol and even with medication for anxiety etc... wouldn't be able to stop) and aren't feeling gung ho about the divorce, then I think you should wait and see...
But again, that's just my 2 cents from the side of the fence of not having had to wonder what to do since my AH has never shown improvement...
Wishing you and your W well...