You might have broke the guy tbh.
That is my suspicion, also.
It's just so odd that he keeled over at that particular point in the game. Incidentally, I found some discussions on Reddit indicating the same thing did happen to others. The assumption there was that Halsin happened to eat a missile from the Shadowfiends during the Isabel/Marcus fight... but I completed that before causing Halsin to come to the Inn.
I can only imagine that since I didn't entirely eliminate the Goblin leaders—I left Minthara alive—the game treated that particular threat as unresolved and the attack on the grove as the inevitable consequence. Now, I've no idea what happens to Halsin if you choose to destroy the grove with Minthara and the goblins, but I doubt that he would join your camp afterwards. So maybe the game flagged him as a casualty of that battle even though it never took place in my playthrough? If that's the case, it's still so weird that this, uh, alternate reality fate caught up with him with such a delay...
