Im afraid I can not agree with your assumption that the Borg are stranded Zombie. For all intents and purposes the Borg have treanswarp capability and if I do recall corectly in Voyager they still have one more of those wormhole cluster nexus thingies. Or is it 2? Even without a queen the borg would undoubtedly have backups in case unimatrix 01 went down. Im afraid with all the data that the federation got from Voyager it would seem to be a tragic tactical error of the federation to dissasemble the taskforce in light of the knowledge they have gained from seven and the rest of her crew.
Im not saying that this is a bad choice by the developers and that it shouldnt of happened, In fact it seems to follow along with the direction starfleet is going, making rash and not intelligent decisions because they are blinded by the aftermath of the dominion war and the unstable situation with the romulans not to mention the ongoing tention with the klingons and khitomer. I must applaud the developers on their story line it seems to be true to form and quite logical.
Guys, you're missing the point both Zombie and I are making. It's not about whether the Borg will come back or whether they have the capability to do so. Since we see them in the trailer, clearly they find some way to do so. That's a given. What you're not thinking about is Starfleet's perception of the Borg's capability.
Even if Voyager had only destroyed the transwarp hub, Starfleet would still probably take this stance. Seven of Nine stated in the episode that there were only 6 hubs in the galaxy, yet the visual showed only 4, one for each quadrant. The Alpha Quadrant one looked less developed than the others, which makes sense as the Borg have not infiltrated that on any scale. Voyager destroyed the Delta Quadrant one, which we can assume would be the most important and first one built (due to the Delta Quadrant being the Borg's home territory). Destroying even one hub kills so many conduits that you severely limit Borg transwarp transportation alone, but since Voyager seems to have destroyed a very important one, it would be very hard for the Borg to send the majority of their forces from the Delta Quadrant to the Alpha. They might be able to send ships back to regroup in the Delta, but sending an attack force from the Delta doesn't seem likely.
And this is not even taking into account the virus. Granted, the Borg will adapt quickly to it, but in the meantime it seems to have severely scrambled their ability to communicate and coordinate, making those far flung ships that aren't in the Alpha Quadrant somewhat confused and without a commanding authority.
So you can kind of see why Starfleet thinks the Borg are at least wounded badly, and will take some time to recover, let alone get their forces here. That's not to say they have absolutely no defences and no plan should a Borg incursion occur. They simply don't see it as efficient in keeping around a specifically Anti-Borg taskforce when the ships could be used for more general defense, research, or science/diplomacy. Now granted, we all know this is a mistake on their part, but if you want a better analogy than the ones that are getting thrown around in this thread, it'd be like the U.S. keeping the Star Wars program and continuing to fund it after every other country dismantled their ICBM's (an almost impossible scenario, I know, but this is supposed to be hypothetical). Is it a nice, advanced defense to have around? Sure. Could someone potentially build another ICBM? Probably. But there's no way we can effectively spend towards and anticipate every single threat that comes at us, so we have to pick and choose for the current scenario.
Remember, don't look at this from our informed 3rd-person omniscient perspectives. Look at it from the shoes of Starfleet brass, and what's the best thing to do with the information you currently have.