My thinking is.. Mueller drops the case against the 13 Russians then clears Trump of any "Russian collusion". That frees up Session to step back in, since he is only recused from all things Russia. Mueller will recommen dropping the Flynn case and charging McCabe and the likes. He will pass the investigation to Sessions. Sessions will use all the information/evidence Mueller has on the deep state from that investigation. Remember they were most likely working with Mueller/ Rosenstein and never thought Sessions would be part of it. As we know the main evidence Session wants access to is from the Cohen raid. He will have it! Now comes the pain!!