Looking at this well to be honest with this situation I wouldn't be fully content with just escaping this city it would be nice to also get the chance to fight back in ways against the joy.
Like setting fire to crates of joy or sabotaging something that dispenses it. These could be high risk tactics but they could give the player long term advantages in the game like as you sabotage and destroy joy caches or storage containers of joy the city starts to feel the loss of joy as their is less and less to take and thus you can see the citizenry slowly act not like normal as joy comes in short supply and more downers start to pop up due to the lack of joy. and thus also give the player more room to maneuver and to get into areas they normally can't.
It would also be nice to even use the drug's effects against itself. Like how certain drugs affect each other in different ways. If you can make some kind of gas drug that doesn't do much to someone who stopped taking joy but if a Joy taker breaths it it can create some kind of reaction similar to other junkies. Like maybe an effect that produces the opposite effect that joy is suppose to do like a massive feeling of depression or guilt, or fear or anger it would depend on the drug but it would be interesting if the player would be to find ways to combat the druggies by exploiting the drug they take.
I could even picture contaminating joy in the game with some kind of drug that render's it's effect useless or something like that.