IF I have a perfectly elastic supply (horizontal), and the unit price of cigarettes goes up by increasing cigarette tax from 8 cents to $1.50, I know the quantity demanded goes down, but what happens in the long term (specifically in regards to tax revenues of the city?)

I'm not sure if you are asking for help in solving a simple and specific economics problem (What happens to tax revenues in a community if they raise taxes on cigarettes?) Or a more general question involving the character of the long run demand for cigarettes in light of government policies. That is, does the future for cigarettes change if there is a large increase in prices today?

In the simple case, I suggest you draw supply and demand diagrams and "model" what happens to revenues if the tax rate rises from .08 to 1.50.

I hope this helps.