Doug McCrae
Legend
There have always been BBEGs, boss monsters, end-of-level baddies, whatever you want to call them. Hill giant chiefs, evil high priests and the like. I can't think of a single Gygax dungeon that doesn't have a Nosnra or an Acererak or some such. When the players fight one of these dudes, it's a climax, even if you're running the most open sandbox ever.Story was not as important as it is now, the story was the result of the PC's actions rather than something they discovered along the way. The upshot of this is that climaxes are not really preplanned events, but rather self-creating based on the ebb and flow of gameplay. And if you look at the old school mega-dungeon style of play you can see that there is no real ending in sight and in such an environment you really limit the IWB's ability to short circuit a carefully planned storyline or mounds of hard work.
It really isn't unplanned. When the DM sets up a dungeon, it's pretty clear where the Big Fights are. This isn't to say that a random encounter with some nameless will-o-wisps can't get out of hand and end up in a TPK, but it's not the fight the players are anticipating.
Sure, there's no final end in a mega-dungeon but there are lots of little endings.