It was always my intention for Sunset Empire to lead to this point -- to climax with the vampires seemingly having won, taken London and driven to the player characters to a very dark place indeed. The point being to raise the stakes as high as possible, then see what happened next.
See, the thing about the heroes of Sunset Empire is that they are all, as I've said in previous entries, excellent case studies in how imperial power crushes people down. None of them have a personal stake in propping up the existing power structures, and indeed many of the characters would be just fine with the world they know being wiped clean.
The question is, when these characters have an opportunity to literally change the world -- what will they do with that opportunity? What kind of future will they build? Will it look like what came before? Will it be a brave new world? Or will they wash their hands of the whole problem once the vampires have been dealt with?
There was an assumption on my players' part earlier in the campaign that this was a game that would fit neatly into the Buffyverse canon, and indeed I have done my best to see that a lot of the elements would work within that framework -- but only to a point. I always remained quiet when they made that assertion, because I knew that my third act was something that would have been impossible for the Buffyverse to ignore or forget. And it would indeed have the possibility of changing the setting forever. (It's a pedantic point anyway, as the Buffyverse never made mention of a Victorian space program or steampunk golems or a large settlement of faeries living inside London. Never mind.)
The discomforting thing (for a GM) about creating such a third act is that it places a great deal of responsibility on the shoulders of the players. I have a great deal of faith in my players' abilities to "bring the awesome", but I have played in a great many games where players balked or froze up when presented with the opportunity to make big, bold moves. They preferred the comfortable presence of a series concept that was smaller in scale and more personal.
But there's nowhere to go but forward, full steam, now. Jump on Mr. Fogg's airship, grab your sword, and get ready to kick out the jams one more time.
God save the Queen!