In the trailer, Harry confronts Ebenezer, and Ebenezer tells him he can't be this stupid. Harry prepares for combat. Implication: He's going to try a hard escape for Thomas.
In the sample chapter, Harry and Ebenezer are suddenly hit with nausea and disorientation, and the corner hounds appear.
WAG:
These scenes are back to back.
Butcher has set Harry up to break all the Laws without "really" breaking the laws. The werewolf belt he didn't make, the self-defense killing, etc.
Butcher effectively engages in destroying or inverting tropes in Dresden Files- it's kind of his thing.
So, I'm going to guess the following:
Whatever happens with the Cornerhounds, Eb dies. But his death leads Harry to solving whatever the crisis is.
And at the end, Harry goes back in time . . and does nothing. His very act of time traveling summons the cornerhounds. He then returns to his own time.
Why? Because the trope of time travel is "what happens if you go back in time and kill your own grandfather?"
Well, if you're already born- nothing.