I think from what I am getting from the story so far is that Bob Reynolds aka the Sentry is a fake so to speak. The Void is what the serum created and Bob Reynolds didnt like it and created the Sentry so he could say he was a hero. Reynolds wanted to be hero but in reallity he never was a true hero deep down inside he always was the Void. The hero part of Reynolds personality is why he is mentally ill. Hence which is why the Void tells him let me take control and things would be better. There never really was a sentry it was just created to hide the Void which he really was. Bob did everything in his power to prevent the void from coming out, but in the end he like the Void seems to have shown he couldnt hide what he truly was THE VOID.
As for stories I think the Void is going to become a major threat on the level of a Galactus or Dormammu in that its going to take the most powerful heros on Marvel earth to stop him.
So maybe Bob is really... Satan? (echo... echo... echo... Church Lady).