Not only can you break quests, but you can break animations.
If you haven't experimented, kill everything. You'll find that some NPCs will die, but they won't become a gory mess. They will still appear on the minimap and continue to move around. You just can't talk to them.
By the way, if you haven't yet done it, NecroShift into the dragon rider early in the game. He's so much faster than the frogs, but his sight is incredibly limited.
