I really think Mueller is twisting in the wind. He's scrambling for leverage against Trump to be able to come to the table and call a halt and neutral truce to this fratricide. But he's coming up short - hence his continuing reaching further and further away from the nexus of this "investigation." He doesn't have the goods on Trump and he's franticly going about trying to find something - anything that he can pin him on. Trump's just sitting back and saying, "F-U! F-U! F-U!" and until Mueller gets something he's going to keep going... until 2020 if necessary.
If Mueller drops the investigation, the IG's report is going to wipe his face with the excrement that Comey and McCabe have just shat out for all the world to see, and his blue pin-stripe suits are going to get sullied in the process. It's a bad day for the FBI and the DOJ. But, they've got it coming, and they've earned every bit of what they're going to get.