Thank you all for your words of wisdom. At this point it seems as though I will just have to wait and see how everything goes after his time at rehab. We told my daughter from the start that my brother was an addict. At her age she is well aware that something is going on, and we didn't want to her to overhear conversations about my brother and then be scared or confused. We told her in a matter of fact way, and have been straightforward with what is happening (with careful editing of some details that we believed to be inappropriate for her age). She is uncomfortable around my brother, and we do not force her to be around him if she is, and it won't even be a choice if he continues to be an active user after rehab.
The most important thing is that I remember that this is not to punish him, but instead to save myself from the frustration and craziness that will only bring me down. I wasn't thinking about it from the perspective of being about me, and was thinking of it as a way to possibly force him to think about his addiction. Thank you for saving me from that train of thought!