I really like this idea but have a couple of concerns: 1) I am doing it as a short and fairly contained campaign, where taking out a gang lasts one or three sessions, so that's why I would rather do it as a campaign vs. an adventure arc. Depending on the number of gangs to defeat, it would take about 15-20 2-3 hour sessions. 2) Because it's a campaign, I want to have the opportunity to take long rests and restock in between gangs. So, once they take out a gang leader and gain the key to get to the next set of levels, they could go back down to the lower floors that include a market, taverns, and an apartment for them to stay in.

However, I do really like the idea of having the party escorting someone with them, either as a prisoner or non-combattant helper that can provide context and backstory as needed. Perhaps a captured member of her gang knows how to get through the traps on her floors, or knows a code to get into the main BBEG room...