Well, the events of Fallout Tactics aren't canon or are very broad-strokes canon at best.
broad strokes. the midwest BoS has been confirmed to exist in dialog from both Fallout 3 and Fallout 4*. whether any of the details from tactics are true is unknown. as of FO3 though, the midwest BoS is MIA so we may never find out.**
*in FO3 you get told by the BoS members that when they trekked across the wasteland from california to the capitol Wasteland, they detoured near chicago to try and make contact with the midwest branch. in FO4 the captain of the Prydwyyn talks about previous BoS airships, which were how the midwest BoS ended up in Chicago.. they were the first attempt to reach the east coast, and their airship flotilla (which was more like the graf zeppelin tech level wise) were damaged in storms and had to put down in the midwest. where they set up shop.
**the same dialog in FO3 that talks about the midwest BoS also establishes that the expedition that became the east coast BoS tried to contact the midwestern branch on their trip across the USA.. and all they got was static.my own guess is that since midwestern BOS styling PA shows up in FO3 used by the enclave (the hellfire armor), and we are told in FO:New Vegas that the Enclave has outposts in Chicago (in the audio logs stored in ED-E), that during the Enclave's trip across north america to relocate from california to the capitol wasteland, that they stumbled over the midwest BOS, destroyed them, and took over the MWBOS facilities for their own use.
personalyl i'm hoping that a future game gets set in chicago and we get to see an enclave, ModWesternBOS, and EasternBOS three way conflict (since the midwesterner's would be viewed as having gone against the ideals of the BoS, since they accept mutants, super mutants, ghouls, and outsiders into their brotherhood, and don't hoard technology as readily.)
