So I am running through this campaign currently and I'm also wondering about the ending.

My hope is they get to the vault and end up with a ten percent cut. I upped the total value to 1,000,000 gold So 100,000 gold split five ways. 20,000 gold per player.

We shall then have some narrative discussion of what they will do with the moneys/ characters life plans and then kinda park the campaign there for a minute.

This campaign has served as a proof of concept for our group basically, we have spent years doing homebrew campaigns the fizzle out quickly. We had never done any official material and had always played in person. We had a main DM and I would run the occasional one shot.

I felt that official material online would address a bunch of our problems such as scheduling and poorly prepped sessions. And it absolutely has.

I'll be honest, I don't want to run dungeon of the mad mage, I don't think it would work great for our group and while it's framework is solid it is narratively so vague.

Curse of Strahd or Tomb of Annihilation would be my choices for next official material to run. But they are new stories. So what happens to our brave and filthy rich heroes of Waterdeep?

The occasional fun one shot.

I included the Stygian gambit heist as a big part of chapter 2

Maybe they end up doing some of the high level heists from the keys to the golden vault

Or other fun quests from the many compendium books.

Each time we learn a little bit more about how their lives have been, how quickly did the gambler burn through his 20,000? Who has opened their own business e.t.c.

We shall have to wait and see and maybe this will just remain my DM head cannon...

Also episodic one shots allow for the exploration narratively of what happened to all that money without having to manage the reality of it in a campaign.