Could a second hive form now?
When the infection was driven out of Will it collected into an airborne mass and crashed through the door to get out of that hot cabin. Part of it was shed and dispersed outside (dead tissue?) but part of the mass stayed intact and went streaking off into the sky. So, what if that starts to grow into a new Shadow Monster? A second independent hive based in our world.
Could be a very bad situation. Not necessarily though; at its current size it probably isn't intelligent yet, but does carry at least some of Will's memories. So the new hive wouldn't be a guaranteed enemy, it might even become an ally. At the very least it wouldn't want the other Mind Flayer crossing over and conquering its domain. That could prove useful even if the new hive is just as hostile as its parent. Any thoughts?