Well, since I'm checking in to make sure nothing changed while I'm pretending I quit the game, might as well make an appearance on a lore thread....
Mistvale is, in fact, an official pack. More specifically, a fallen pack, according to
the History of Loria. The two-leaf symbol, seen on
Korvo's official art as well as I believe a few other locations, is in fact the pack's symbol. Each pack had its own special skill; before its downfall, Mistvale was a pack themed around restoration, which is exactly what made it such a dangerous pack for Chaos to take over - and Korvo being easily persuaded didn't really help. Which is why Korvo and Chaos were trapped at the bottom of Lake Viridia: being surrounded by the four packs was likely the easiest (and safest) way to keep the threat contained, while the Creators and Spirit Wolves returned to the Astral Plane.
As for how the campaign lore would end... I've honestly not really thought about it. Though I would assume Chaos wouldn't be wiped out forever - that would contradict what was said in the History of Loria (that Chaos could never be fully separated from the land), plus would force either a contradiction or a lore rewrite for the seasonal pack events, which (last time I checked) focus on Chaos returning to Loria. So Chaos would always be a threat to Loria, even if he was trapped again.
I could see Korvo being saved possibly, though never being quite the same again. But that being said, I don't think anyone's ever said anything about ever being able to join Mistvale as a pack (unless that happened and I missed it), and from a lore standpoint it sort of makes sense that lorwolves wouldn't want or be allowed to live in the land where Chaos is being held. I do believe that the final chapter of the campaign does allow us to at least explore Mistvale though, or at least it's supposed to based on the last thing I heard about it.
spoot
