I think Regina is going to take a backseat to Rumple as the big bad this season. After seeing “Broken” I think is is more focused on getting Henry back then getting revenge on anyone now, and Henry has made it clear that he doesn’t want anything to do with her if she’s still evil.
Rumple has already shown that he takes longer to learn his lesson and it will be interesting to see what happens when he has both Bae and Belle to act as morality pets. But even then I think it will take at least a season or two for him to change.
And the Charmings, Regina and Rumple may all have common ground in Henry if Bae is his dad. It would be interesting to see a plot line where they all have to work together to save him.
Don’t worry though, there are plenty of people who can act as big bads in seasons to come. There’s the wicked witches from wizard of Oz, the Red queen, and maybe even the white witch from narnia (probably not, but it would be interesting to see none the less).