Expecting Misty to come back in BW has a really low chance of happening. All I'm looking for is at least a mention of her. Anything really ^^; But maybe when Ash is done traveling in Unova, he could meet up with Misty back in Kanto :D
I just realized that Ash had to return back home before even getting in the plane to go to Unova. So maybe off-screen Ash and Misty met up with each other one more time. I don't think Misty would want to see Ash if she had a chance.