I honestly don’t see why Rumpel would release all that magic knowing that it would give Regina a leg up. It makes no sense. I think he released it knowing that everyone would be able to use it except Regina.
I don’t think Rumpel cares whether or not Regina gets her magic back. He has his own agenda and Regina was just a means to an end.
I think it would be more interesting if Regina did get her magic back, it means she can play a lot dirtier when fighting with Emma over Henry. Before the magic had returned, Regina was defeated and had given up. However, the look on her face when she saw the purple smoke suggests that she knows what is happening and that Emma had better watch out because Regina is back with a vengeance.