The following article contains spoilers from DC vs. Vampires #7, on sale now.
With the new vampire regime in complete control of the Earth, the few surviving heroes are scrambling to devise a counterattack plan. However, DC vs. Vampires #7 (by James Tynion IV, Matthew Rosenberg, Otto Schmidt, and Tom Napolitano) showed readers a rebellion plagued by infighting as they debate the best course of action. Shockingly, one of their smartest members, Batgirl, offered the solution with the least likely chance of a successful outcome, win or lose.
Her plan boiled down to going to Gotham City and killing Dick Grayson, the current vampire king. In a standard war, this could very well be a sound strategy. However, in this supernatural conflict, there are numerous complications. Moreover, even if the heroes achieve the goal of a slain vampire king, it seems unlikely to truly fix anything.
One thing that became abundantly clear about the new vampire kingdom is that there is a clearly defined hierarchy. Vampires exist in a system of succession from top to bottom. Dick has already confirmed that a designated successor should something happen to him. Thus, even if Batgirl succeeds in killing him, it will only give the vampires' a momentary pause before they turn to Grayson's "heir."
Worse, the heroes have no idea who this successor may be. It isn't clear to what extent they'll share Nightwing's vision of a new world order. Whereas Grayson has shown moments of compassion for Damian and Alfred and has even expressed the idea of some sort of eventual coexistence between people and vampires, there's no guarantee the next vampire monarch will even possess that tiny shred of humanity. This unknown successor could do away with the careful balance Nightwing was trying to maintain the balance between humans and vampires and initiate a genocide. Without Grayson's guidance, the vampires might become even more aggressive than they already are. The surviving heroes may rapidly learn the meaning of "better than the devil you know."
This all hinges on it succeeding in the first place, of course. Batgirl may be one of the most competent people on the planet, but Nightwing has outmaneuvered everyone so far. There's no reason to expect he doesn't have a contingency in place if any of his surviving family members decide to seek revenge. Then there is the fight between Nightwing and Damian Wayne in DC vs. Vampires: Hunters #1 (by Matthew Rosenberg, Neil Googe, Antonion Fabela, Troy Peteri) to consider.
Damian's attempted assassination of Nightwing went wrong almost immediately. Nightwing let him escape, but he made it clear that he had taken measures to protect himself. If someone who Batman trained says that there will be no getting to him anymore, then it's going to be all but impossible for Batgirl to pull it off.
So, then why would she want to take such a risk? The unknowns of the mission are enough to give anyone pause, and history tells her that going directly after Nightwing doesn't work. The only explanation is that she's letting her emotions cloud her judgment. Harley Quinn likely informed the rebels how she acquired Lex Luthor's blood and what became of its heroic deliverer. This means that not only did Dick Grayson betray her, not only did he kill Batman in cold blood, but he also created a situation that led to her father's murder.