To tell the truth, I have plans on different stories for Dungeons, but I can't DM. If anything I would love to find a Group that would allow a Storyteller to control the story while a true DM brings in the Mobs/Dice/Etc. The Storyteller and the DM talk between campaigns on what should appear in the 'chapter' and what shouldn't, where there should be such and so on. Kinda like those pregenned campaigns. The main idea is that the players are actually charcters in the storytellers tale, they affect the tale that is being told in a past tense kinda way to the background characters in the 'present' time. But the thing is the 'Children' listening to the Tellers story, change things...
Hands up if you have planned a Campaign as a DM and it goes the wrong way like crazy due to your players had gone left instead of right. Its kinda like this. The Storyteller adapts the tale to fit in the Childrens additions. ^_^
Here is how I would do this.
The Party are a few Dwarves that had been recruited to discover what had happened to the MountainHome of Boatmurdered. They clear a 'Chapter' which gives them access to the front area of the Fort's map. In this they fight Goblins that had camped in the Fort where they could reach while they gather what Dwarven Loot they could gather but unable to get deeper due to caveins and Magma Rivers and such. At the End of the Chapter the Players get their goodies, level up and where normally they would go back to town to restock, they actually discover that More Dwarves have come to the fort and have started to recover the Fort...
During Downtime the player's characters helped refurbish the reclaimed area, homes are redug, stores pop up and a small 'hamlet' starts to grow again.
What happens then is that the Teller gives the choice of which tale to tell next, this will begin Chapter 2. This chapter extends past the Cavein or across the river, extending the dungeon on which they can crawl, recovering more of the Fort for the City to recover, giving them more to fight, explore and in the end advance the Fort through growth to give them better goods to purchase and such...
As this goes on you could reach the Chasm as early as Chapter 3-4 or even later if the players choose to explore the Stories they didn't choose. When they Reach the Chasm they can then 'unlock' default campaigns where they go into the Chasm which extends into something different and such. Something that the DM could run without the Teller because it doesn't effect the upper fort. Reaching the Magma Forges gives access to greater gear and Reaching the Hell pits give access to the lovely Candicane Armour and Weapons that have been lost in the Pits after the Deamons dragged their original wielders back with them. And if the player dies, they can easily become on of the Dwarves from the Fort, joining the original party with the similar skills (But stock equipment)...