I imagine that a lot of people would simply give up on blood altogether. While many of the people on here are very serious about their lifestyles, I know that a lot of 'vampires' are simply fad followers. The lifers would just get around it. The methods have been mentioned: psy energy, animal blood, their own blood, abstaining entirely, or becoming violent.
It doesn't particularly matter which method they would choose, since they don't literally need blood to survive. It's a mental need if anything, but not a physical one. Any illness or discomfort caused by that lack would have to be psychosomatic in nature. If it continued long enough, they'd simply be hospitalized until they could get the help they needed.
As for those who would turn to the more unpleasant methods, well there are already people like that around. Like them or not, they are part and parcel with the vampiric community as a whole. Every member follows the ideas of the fiction to some extent, these ones just follow it a bit to closely for comfort.
Although other members of the community might not want to be tarred with the same brush as these people, they also must accept that they have little choice in the matter. If they call themselves vampires, then no one else in the community has any right to refute that claim, nor is there any argument the community could make against them that could not also be turned back on themselves to refute their own claims to vampirism.
Simply put, the vampire community is diverse, and the people in it will always have different ways of dealing with the things that affect them. Each person has a different set of morals, beliefs, and ideas, and so there's no telling how each would react in a given situation until they have been put in it.
