Starting a New Campaign
I don't really see how that's going to help, as the players behind the PCs will still be the same. WHY do they compete with each other to see who slays the weak critters? WHY do they argue over treasure?
I guess the first thing I'd do would be to sit down with each player, at a separate time & place, and ASK them those questions. Why won't they work together? Once you know the Players' views, maybe you can do something about it.
If not, then I, too, would let the vampires win, play a last few sessions of "running and hiding" (or "fighting and dieing", if the players prefer), and then tell them you're putting this game on "Pause" while you start the new one. Then I'd use the idea, above, with first level PCs in one of the last free cities, with Vampires all around, but with a
few additions...
The "old" PCs from the last campaign show up as Vampire Lords, leading the new armies! The defenders of the city have until nightfall to do SOMETHING, so they scry and divine, and find out that the "web of events" that lead to this current-day problem follow from what happened 250 years ago, about a week in the future of the "old" timeline...
The City can't/won't risk defenders on trying to go back and change time, but one of the Mages has a magical mirror that can send a small group back in time... but it's a one-way trip, and no one is crazy enough to try... and night is coming!
The City has no hope of surviving the vampire invasion. The Mage has a way out, if anyone is crazy enough to risk going back, 250 years into the past, on a one-way journey to attempt the "turning" of the Vampire Lords...
If the first level PCs volunteer, they get sent back, with a scroll, and the mirror shatters behind them. The Mage's scroll introduces him (and in the "old" campaign, he is "just" a child prodigy, at this point, but the PCs
have heard of him, and great things are expected). Anyway, the scroll details the events of how they not only
die in two weeks, but are also
turned into vampires, who will be leading the assault on the city in 250 years!
The scroll details all of their actions, points out the mistakes, makes suggestions for what
could have worked, and while it paints the PCs as having died heroically, it also tells what they did for the next 250 years, in gruesome detail, including how they "turned" their own families and former lovers, and sold themselves out, heart and soul, to evil...
After reading the scroll to them, let the PCs react for a bit, then remind them that
they are playing the first level PCs, and that
you are playing their "old" PCs as NPCs! Let them try to convince their "old selves" to work together,
while you play their old selves, listing all of the reasons why they won't!
Make the new PCs try to convince the old ones, and remind them that, they know how tough their old 12th-level selves were, and how little chance these new, first-level PCs would have against them in combat!
If they still attack, let the first level PCs all die, then pick up with the old campaign... If the new PCs try to convince the old, at some point, you should turn the decision back to the players... Of course, if they continue as always, I'd just let'em get vamped, and be done with it...
...Then I'd go look for some new players!
Otherwise you could have history repeating itself.
