I'm not sure if Bill still has the power to order Warlow around, he was almost drained dry and then he rejected those 3 bloody women when they tried to take him back to Lillith, so he may not be able to still command Warlow around like he did before. But then again, he just might, so who knows.
I really hope Niall comes back for the final episode, Rutger Hauer was awesome as Niall, I miss him and Jason together, they were just so good as a team.
I think he would still be able to have powers as Warlow's maker. The show has never shown physical injury to impair the maker/progeny bond. Still, this is True Blood and nothing is sacred.