Not really, they are both equally important for him. He coulda just take the usual way out and kill Hannah.
Hannah said to him too as she was taken away "You should have killed me!" Sure Dexter is keeping Deb safe by getting her put away, but the risk in doing so to his secret and the fact of leaving here there after she told him that would surely indicate Dex will kill her, out of love for her and to protect his secret.