Assuming Brock wins at SummerSlam & walks out that night with the title(s) (I'm 99% sure that's going to happen), I don't see him dropping it at NOC at all. That would seem like such a waste of having him win. If he gets it from Cena at SS, he's holding it right up to WrestleMania & maybe longer (but probably not). Having him as a champion up until WM would be a great draw for the Network as well, especially if he "doesn't fight for free", meaning you'll only see the champ wrestle at PPV's. He can rematch Cena at NOC & retain. Then maybe annoy the Authority by not listening to them, resulting in a match with someone on their side. This person could either be Orton, or possibly Cesaro, who wants to beat Lesnar to show Heyman that he's the #1 client.
Eventually Lesnar will cross paths with Reigns (assuming all goes well with his build. I think it will). Roman could win the Rumble & start it that way, or have him challenge Lesnar at TLC, with Lesnar having to resort to some shenanigans in order to retain. This can then make Reigns' Rumble win & eventual WM win even more triumphant.
As for Seth, I still think it's too early for him to cash in, and don't think he should do so until after Wrestlemania. The thing with him and Dean could last up until Wrestlemania if they continue pushing it the way they have been with the whole "I'll always be there when you cash in" stuff. Then with Reigns as the champ, have Rollins cash in on him, and throw Ambrose into the mix, and you have a nice triple-threat feud to keep things interesting post-WM.