And best of luck with it. I don't like PbtA myself, but Masks is one of the better ones I've seen.
Incidentally, I had a thought while at work: has anyone ever tried to use Microscope or similar generators to run a nonlinear RPG campaign? I mean something like Call of Cthulhu Through The Ages but as a coherent campaign spanning the entirety of human history, presumably democratically deciding which leads from the previous scenario get expanded.
To continue on from the previous example, if your investigators foil the present incursion by the Mi-Go with the help of a mad professor's analysis of Middle Paleolithic cave paintings, perhaps the next couple sessions are spent playing the professor, or the Neanderthals who originally painted them -- and perhaps the Elder Things that helped them figure it out also tried something in ancient Rome, and the Nyarlathotep cultists who found the mad ramblings of the investigators who stopped _that_ bided their time until the 1920s, at which point they were defeated until the stars were right again in 3056 and so forth. Or maybe it was the investigators who were sealed away until then.
Gradually you'd build up this whole mythos of humanity's millennia-long struggle against the eldritch horrors, and it'd keep a feeling of continuity despite a high body count -- and it'd actually let the investigators fail, because when they do, well clearly they weren't actually the ones to stop Hastur from taking over the world. Clearly it was these other folks who carefully edited the cultists' books a hundred years ago to replace the summoning ritual with show tunes translated into Welsh or something.