Well, they've been assimilated by a race even more powerful than the Borg.
I think if the Borg assimilated all the inhabitants of the Earth, technically speaking that would mean the end of humankind. Although we might live on as Borg drones, I think humankind would be dead.
But, and this is the bigger but, if a species lives on as part of another one after they've been assimilated, they cease to exist as the main villain of the show. This is what I find to be one of the worst things about the relaunch books. Technically speaking the borg might not be dead but in reality they are. The have been assimilated, which to me is synonymous with "destroyed". In the state they are in now, it's virtually inconceivable that they can pose any kind of threat, which means that one of the best - if not the best - plot opportunities is lost. Voyager has always been the big borg show to me, Voyager has also always been the show about a starship lost in space and the relaunch books took all that away from us.
Not to mention the fact that Voyager is not alone now in the DQ but heading an entire armada. Where's the sense of being lost, the sense of being alone? Lost ... somewhere in the writing.