I used the above-ground Vault with the new underground Vault mixed together by replacing the room past the Counting House with a inner-courtyard-style structure. It suggested that the Bank had been build over, and around, the dwarven structure. As an ending to Dragon Heist it allowed for a session comprised of a interesting mix of sneaking, planning, and conning (like a proper Heist!) topped off by a finale with a literal Dungeon and a Dragon. The key element allowing for this was the wonderfully detailed Bank Worker information, as well as the clockwork nature of the bank's systems. I provided players with all of the Bank Workers info ahead of the session, which let them start constructing a plan and consider the bank as a fully realized building.
A terrific addition to the slightly anti-climatic conclusion of an otherwise great published adventure.
[5 of 5 Stars!]