It won't be immediate and it really shouldn't. Looking at the children's best interests, there needs to be a phased in reconciliation. Brad will need to adjust to being free and the children spent some formative years not knowing him. They will need a lot of counseling and time to re-establish their relationship. Also, the Rentzes still have a claim to at least visitation with the children, and I think that should be granted, assuming they were good care givers and did not action in violation of the court order in regards to discussions about BC or NC. I trust the Rentzes handled this appropriately, I'm more skeptical about KM.
Now, if BC were to move back to Canada, then jurisdiction should rightfully so be transferred, as there would no longer be any parties to the action in North Carolina. But so long as BC stays in North Carolina, jurisdiction stays in NC. And I also believe that Canada is a signatory the Hague Convention, so should they refuse to cooperate with North Carolina courts, BC would have remedies available through their international child abduction compacts.
I don't know how Canadian courts deal with custody, so I couldn't even begin to advise BC on the best forum to deal with this. It's apparent the Judge in the custody matter didn't like BC to begin with and I'm not sure how she'd react with egg on her face. She will be the judge in any future proceedings, assuming she's still on the bench, although I'd imagine a motion to recuse would be filed.