I disagree. Raiden is a god, and is immortal. He sacrificed his powers to try to stop the Dragon King, but it didn't work. He is simply torn up from the power that was released from him. In the videos we see he still has lightning surrounding him so he must still have some of his 'thunder god' powers. I believe he is just weakened from the sacrifice he made. He might be restored to full power by the Elder Gods in his ending. We'll just have to wait and see.