Or vice versa. After all, if the Borg truly failed, wouldn't they try again? That's sort of inherent in time travel.
Queen: "My brilliant plan is to erase the Federation by tampering with their past. I will execute it tomorrow. I definitely will."
<cybernetically augmented crickets chirp>
Queen: "Oh, well, apparently I didn't succeed. Okay, so my NEXT plan is to try even harder with erasing the Federation by tamperi... Wait, what am I saying? What is 'Federation'? Ah, no matter. Let's move on to the next item. Assimilation of Earth. You say it's a primitive world not worth tuppence?"
Drone #74656: "Indeed, my liege. Shall we proceed anyway?"
Queen: "Sure. In 6,300 years or so, when they have evolved enough. Do they have any interesting neighbors?"