Thanks for playing the game and sharing your thoughts! That's a bug. When there are no more regions, it should hit the win condition. It sounds like you hit a situation in which that failed to register. If I have a chance to revisit this, I'll fix that bug and add a random 1-2 extra turns to unassigned quests. I think that will address the issue sufficiently while still requiring the player to choose a region every turn. However, once a group of heroes has embarked on a quest, I'll stick with the current rule that you can't add more heroes. Part of the challenge is committing the right number of heroes from the start, or taking the hit and losing a point of renown if you leave it unassigned. Some play sessions may just be more easily winnable than others depending on the random allocation of region events.
Regarding the bug, upon completing what I could of the map, three tiles remained that would highlight if I moused over them, but could not be selected and didn't have any graphics indicating a challenge to face there. At first I presumed these being empty was just the result of randomization, i.e. that some lands could generate with no challenge and that was fine, but upon subsequent play-throughs, I've noticed it was the same lands that were again highlightable but not selectable (though most everything else had randomized). Perhaps there is some problem generating content for certain tiles? If it helps, these are the village three tiles northeast of the starting castle, the shire to its immediate west, and the mountain on the northern edge of the northeast corner of the map.