After plenty of amazing and no-so-amazing moments, the DH campaign I've been DMing is coming to a rather anticlimatic close.

The party of four (they call themselves The Trollskull Gang) figured out the vault puzzle and met Clanghammer/Aurinax, they ran hard into a wall. I used a variant of the skill checks outlined for persuading the dragon in disguise so that they need to pass five of eight DC 15 skill Persuasion checks. If they fail more than three, the dragon in disguise stops believing anything they say and gets annoyed (but doesn't attack unless directly threatened or if they try to steal the gold). The sorcerer with the high Persuasion modifier failed three checks in a roll (including one made with advantage). So, at this point, my backup plan kicks in: Raener Neverember. The party actually, kind of smartly, asks the Stone of Golorr for more information, and it suggests that a familial connection might sway the dragon. They left Raener waiting outside the crypt with the carriage, which they then convinced him through more checks to come down into the vault.

"OK," I thought. "They got the big gun. One more skill check with advantage." And they completely, utterly fail. Not even close. *deep sigh*

Fortunately, it was near the end of the scheduled session. But it definitely was anti-climatic. Out of game, all of the players mentioned how they could attack the dwarf/dragon, but they all know enough of the game (both in and out) to know they'd likely be TPK'd. They do have the backing of the Grey Hands, but they found the treasure and know they have to turn over that information. That means any expedition back to the vault is going to be taken over by The Blackstaff and maybe other powerful people in the city to negotiate the release of the gold.

I do plan to leave the next decision up to them: fight the dragon or return to Blackstaff. Either it's a likely TPK or some railroading that eventually leads them to get the 10 percent finder's fee (but they don't know that yet).

My question: Is the main adventure effectively over at this point? Can I railroad a bit (if they don't get themselves killed) so that the Grey Hand/city officials take over the gold recovery operation? And leave the party to clean up the loose threads, like the Cassalanter's cult or the remaining members of the Xanather Guild?

I'm thinking about hosting a Session Zero 2.0 and just come out and say that, regardless of what they do next inside the vault, they "finished" Dragon Heist -- uncovered a mystery, sussed out clues and found the gold.