The likelihood of exposure has been set out on other threads, but thousands die, more are injured and their medical bills and funerals are paid by Mab
Harry has made it clear that this is too big to dismiss, and he took the Placard with him, a communications device.
It is presumed that Harry is sucked into the other universe, but we don’t know for how much of the book, as first person narratives the books happen over a couple of days. I suspect evil Harry will look at our Harry and think he has the best of it (he won’t fool Mouse).
In Grave Peril Harry was able to take back the part of himself stolen by The Nightmare, it may be that the two Harry’s end up in a battle where they are fighting for their joint power, winner takes both as there are not supposed to be two of them in the same world. That would give Harry a major power up. Something similar occurred with memories in Ghost Story, so I suspect Harry ends up with twice the power and two sets of memories.
WOJ is that it was a decision in Grave Peril which changed the course of history, since that WOJ we know that alternate worlds are created by time travel from Vadderung/Kringle. Could alter Harry have time travelled back to save Susan and the Dresdenverse be the other leg of this particular pair of the trousers of time creating the split.
If Murphy dies in Battle Ground does he bring alter Murphy back with him? At this point In Grave Peril Murphy was a lieutenant at SI, Harry hadn’t brought her into the supernatural world, she may without Harry have been cashiered much earlier in her career (Rudy) and have very little in her life, no career, two failed marriages, Chicago gone to hell from the two times their Harry didn’t save the world. They end up having to re-start their relationship all over again. Jim gets to have his dead Murphy cake and gets to eat it. Always go with what will make Harry suffer the most. He will get to see Murphy, his old Apartment, the Blue Beetle
The alter Bob would still have the Kemmler memories. Kemmler was suspected of timetravel so that alter Bob may be have the info Harry needs to get home, so I suspect alter Bob will also come to the main continuity. This may explain why Kemmler got so powerful, he had the power of several Kemmlers.
If alter Mister is left without a Harry then Jim will never be forgiven.